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This is gnugo.info, produced by makeinfo version 4.11 from gnugo.texi.

INFO-DIR-SECTION GNU games
START-INFO-DIR-ENTRY
* GNU Go: (gnugo).          The GNU Go program
END-INFO-DIR-ENTRY

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File: gnugo.info,  Node: The Owl Code,  Next: Combinations,  Up: Pattern Based Reading

12.1 The Owl Code
=================

The life and death code in `optics.c', described elsewhere (*note
Eyes::), works reasonably well as long as the position is in a
"terminal position", which we define to be one where there are no moves
left which can expand the eye space, or limit it. In situations where
the dragon is surrounded, yet has room to thrash around a bit making
eyes, a simple application of the graph-based analysis will not work.
Instead, a bit of reading is needed to reach a terminal position.

   The defender tries to expand his eyespace, the attacker to limit it,
and when neither finds an effective move, the position is evaluated. We
call this type of life and death reading "Optics With
Limit-negotiation" (OWL). The module which implements it is in
`engine/owl.c'.

   There are two reasonably small databases
`patterns/owl_defendpats.db' and `patterns/owl_attackpats.db' of
expanding and limiting moves. The code in `owl.c' generates a small
move tree, allowing the attacker only moves from `owl_attackpats.db',
and the defender only moves from `owl_defendpats.db'. In addition to
the moves suggested by patterns, vital moves from the eye space
analysis are also tested.

   A third database, `owl_vital_apats.db' includes patterns which
override the eyespace analysis done by the optics code. Since the
eyeshape graphs ignore the complications of shortage of liberties and
cutting points in the surrounding chains, the static analysis of
eyespace is sometimes wrong. The problem is when the optics code says
that a dragon definitely has 2 eyes, but it isn't true due to shortage
of liberties, so the ordinary owl patterns never get into play.  In
such situations `owl_vital_apats.db' is the only available measure to
correct mistakes by the optics. Currently the patterns in
`owl_vital_apats.db' are only matched when the level is 9 or greater.

   The owl code is tuned by editing these three pattern databases,
principally the first two.

   A node of the move tree is considered `terminal' if no further moves
are found from `owl_attackpats.db' or `owl_defendpats.db', or if the
function `compute_eyes_pessimistic()' reports that the group is
definitely alive. At this point, the status of the group is evaluated.
The functions `owl_attack()' and `owl_defend()', with usage similar to
`attack()' and `find_defense()', make use of the owl pattern databases
to generate the move tree and decide the status of the group.

   The function `compute_eyes_pessimistic()' used by the owl code is
very conservative and only feels certain about eyes if the eyespace is
completely closed (i.e. no marginal vertices).

   The maximum number of moves tried at each node is limited by the
parameter `MAX_MOVES' defined at the beginning of `engine/owl.c'. The
most most valuable moves are tried first, with the following
restrictions:

   * If `stackp > owl_branch_depth' then only one move is tried per
     variation.

   * If `stackp > owl_reading_depth' then the reading terminates, and
     the situation is declared a win for the defender (since deep
     reading may be a sign of escape).

   * If the node count exceeds `owl_node_limit', the reading also
     terminates with a win for the defender.

   * Any pattern with value 99 is considered a forced move: no other
     move is tried, and if two such moves are found, the function
     returns false. This is only relevant for the attacker.

   * Any pattern in `patterns/owl_attackpats.db' and
     `patterns/owl_defendpats.db' with value 100 is considered a win: if
     such a pattern is found by `owl_attack' or `owl_defend', the
     function returns true. This feature must be used most carefully.

   The functions `owl_attack()' and `owl_defend()' may, like `attack()'
and `find_defense()', return an attacking or defending move through
their pointer arguments. If the position is already won, `owl_attack()'
may or may not return an attacking move. If it finds no move of
interest, it will return `PASS', that is, `0'. The same goes for
`owl_defend()'.

   When `owl_attack()' or `owl_defend()' is called, the dragon under
attack is marked in the array `goal'.  The stones of the dragon
originally on the board are marked with goal=1; those added by
`owl_defend()' are marked with goal=2. If all the original strings of
the original dragon are captured, `owl_attack()' considers the dragon
to be defeated, even if some stones added later can make a live group.

   Only dragons with small escape route are studied when the functions
are called from `make_dragons()'.

   The owl code can be conveniently tested using the `--decide-owl
LOCATION' option. This should be used with `-t' to produce a useful
trace, `-o' to produce an SGF file of variations produced when the life
and death of the dragon at LOCATION is checked, or both.
`--decide-position' performs the same analysis for all dragons with
small escape route.

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File: gnugo.info,  Node: Combinations,  Prev: The Owl Code,  Up: Pattern Based Reading

12.2 Combination reading
========================

It may happen that no single one of a set of worms can be killed, yet
there is a move that guarantees that at least one can be captured.  The
simplest example is a double atari.  The purpose of the code in
`combination.c' is to find such moves.

   For example, consider the following situation:


     +---------
     |....OOOOX
     |....OOXXX
     |..O.OXX..
     |.OXO.OX..
     |.OX..OO..
     |.XXOOOXO.
     |..*XXOX..
     |....XOX..
     |.XX..X...
     |X........

   Every `X' stone in this position is alive. However the move at `*'
produces a position in which at least one of four strings will get
captured. This is a _combination_.

   The driving function is called `atari_atari' because typically a
combination involves a sequence of ataris culminating in a capture,
though sometimes the moves involved are not ataris. For example in the
above example, the first move at `*' is _not_ an atari, though after
`O' defends the four stones above, a sequence of ataris ensues
resulting in the capture of some string.

   Like the owl functions `atari_atari' does pattern-based reading. The
database generating the attacking moves is `aa_attackpats.db'. One
danger with this function is that the first atari tried might be
irrelevant to the actual combination.  To detect this possibility, once
we've found a combination, we mark that first move as forbidden, then
try again. If no combination of the same size or larger turns up, then
the first move was indeed essential.

   * `void combinations(int color)' 

          Generate move reasons for combination attacks and defenses
          against them. This is one of the move generators called from
          genmove().

   * `int atari_atari(int color, int *attack_move, char
     defense_moves[BOARDMAX], int save_verbose)' 

          Look for a combination for `color'. For the purpose of the
          move generation, returns the size of the smallest of the
          worms under attack.

   * `int atari_atari_confirm_safety(int color, int move, int *defense,
     int minsize, const char saved_dragons[BOARDMAX], const char
     saved_worms[BOARDMAX])' 

          Tries to determine whether a move is a blunder.  Wrapper
          around atari_atari_blunder_size. Check whether a combination
          attack of size at least `minsize' appears after move at
          `move' has been made.  The arrays `saved_dragons[]' and
          `saved_worms[]' should be one for stones belonging to dragons
          or worms respectively, which are supposedly saved by `move'.

   * `int atari_atari_blunder_size(int color, int move, int *defense,
     const char safe_stones[BOARDMAX])' 

          This function checks whether any new combination attack
          appears after move at (move) has been made, and returns its
          size (in points).  `safe_stones' marks which of our stones
          are supposedly safe after this move.

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File: gnugo.info,  Node: Influence,  Next: Monte Carlo Go,  Prev: Pattern Based Reading,  Up: Top

13 Influence Function
*********************

* Menu:

* Influential Concepts::        Conceptual Outline of Influence
* Territory and Moyo::		Territory, Moyo and Area
* Influence Usage::		Where influence gets used in the engine
* Influence and Territory::     Influence and Territory
* Territorial Details::		Details of the Territory Valuation
* The Influence Core::          The Core of the Influence Function
* The Influence Algorithm::     The algorithm of `accumlate_influence()'
* Permeability::                Permeability
* Escape::                      Escape
* Break Ins::                   Break Ins
* Surrounded Dragons::          Surrounded Dragons
* Influential Patterns::	Patterns used by the Influence module
* Influential Display::         Colored display and debugging of influence
* Influence Tuning::            Influence tuning with view.pike

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File: gnugo.info,  Node: Influential Concepts,  Next: Territory and Moyo,  Up: Influence

13.1 Conceptual Outline of Influence
====================================

We define call stones "lively" if they cannot be tactically attacked,
or if they have a tactical defense and belong to the player whose turn
it is. Similarly, stones that cannot be strategically attacked (in the
sense of the life-and-death analysis), or that have a strategical
defense and belong to the player to move, are called "alive".  If we
want to use the influence function before deciding the strategical
status, all lively stones count as alive.

   Every alive stone on the board works as an influence source, with
influence of its color radiating outwards in all directions. The
strength of the influence declines exponentially with the distance from
the source.

   Influence can only flow unhindered if the board is empty, however.
All lively stones (regardless of color) act as influence barriers, as do
connections between enemy stones that can't be broken through. For
example the one space jump counts as a barrier unless either of the
stones can be captured. Notice that it doesn't matter much if the
connection between the two stones can be broken, since in that case
there would come influence from both directions anyway.

   From the influence of both colors we compute a territorial value
between -1.0 and +1.0 for each intersection, which can be seen as the
likely hood of it becoming territory for either color.

   In order to avoid finding bogus territory, we add extra influence
sources at places where an invasion can be launched, e.g. at 3-3 under
a handicap stone, in the middle of wide edge extensions and in the
center of large open spaces anywhere. Similarly we add extra influence
sources where intrusions can be made into what otherwise looks as solid
territory, e.g. monkey jumps. These intrusions depend on whose turn we
assume it to be.

   All these extra influence sources, as well as connections, are
controlled by a pattern database, which consists of the two files
patterns/influence.db and patterns/barriers.db. The details are
explained in *note Influential Patterns::.

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File: gnugo.info,  Node: Territory and Moyo,  Next: Influence Usage,  Prev: Influential Concepts,  Up: Influence

13.2 Territory, Moyo and Area
=============================

Using the influence code, empty regions of the board are partitioned in
three ways. A vertex may be described as White or Black's "territory",
"moyo" or "area". The functions `whose_territory()', `whose_moyo()' and
`whose_area()' will return a color, or EMPTY if it belongs to one
player or the other in one of these classifications.

   * Territory

          Those parts of the board which are expected to materialize as
          actual points for one player or the other at the end of the
          game are considered "territory".

   * Moyo

          Those parts of the board which are either already territory
          or more generally places where a territory can easily
          materialize if the opponent neglects to reduce are considered
          "moyo".  "moyo".

   * Area

          Those parts of the board where one player or the other has a
          stronger influence than his opponent are considered "area".

   Generally territory is moyo and moyo is area. To get a feeling for
these concepts, load an sgf file in a middle game position with the
option `-m 0x0180' and examine the resulting diagrams (*note
Influential Display::).

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File: gnugo.info,  Node: Influence Usage,  Next: Influence and Territory,  Prev: Territory and Moyo,  Up: Influence

13.3 Where influence gets used in the engine
============================================

The information obtained from the influence computation is used in a
variety of places in the engine, and the influence module is called
several times in the process of the move generation. The details of the
influence computation vary according to the needs of the calling
function.

   After GNU Go has decided about the tactical stability of strings, the
influence module gets called the first time. Here all lively stones act
as an influence source of default strength 100. The result is stored in
the variables `initial_influence' and `initial_opposite_influence', and
it is used as an important information for guessing the strength of
dragons. For example, a dragon that is part of a moyo of size 25 is
immediately considered alive.  For dragons with a smaller moyo size, a
life-and-death analysis will be done by the owl code (see *note Pattern
Based Reading::). A dragon with a moyo size of only 5 will be
considered weak, even if the owl code has decided that it cannot be
killed.

   As a tool for both the owl code and the strength estimate of dragons,
an "escape" influence gets computed for each dragon (*note Escape::).

   Once all dragons have been evaluated, the influence module is called
again and the variables `initial_influence' and
`initial_opposite_influence' get overwritten. Of course, the dragon
status', which are available now, are taken into account. Stones
belonging to a dead dragon will not serve as an influence source, and
the strengths of other stones get adjusted according to the strength of
their respective dragon.

   The result of this run is the most important tool for move
evaluation. All helper functions of patterns as explained in *note
Patterns:: that refer to influence results (e. g. `olib(*)' etc.)
actually use these results. Further, `initial_influence' serves as the
reference for computing the territorial value of a move. That is, from
the influence strengths stored in `initial_influence', a territory
value is assigned to each intersection. This value is supposed to
estimate the likelyhood that this intersection will become white or
black territory.

   Then, for each move that gets considered in the function
`value_moves', the influence module is called again via the function
`compute_move_influence' to assess the likely territorial balance after
this move, and the result is compared with the state before that move.

   An additional influence computation is done in order to compute the
followup value of a move. Some explainations are in *note Territorial
Details::.

   Some of the public functions from `influence.c' which are used
throughout the engine are listed in *note Influence Utilities::.

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File: gnugo.info,  Node: Influence and Territory,  Next: Territorial Details,  Prev: Influence Usage,  Up: Influence

13.4 Influence and Territory
============================

In this section we consider how the influence function is used to
estimate territory in the function `estimate_territorial_value()'.

   A move like `*' by `O' below is worth one point:

     OXXX.
     OX.XX
     O*a.X
     OX.XX
     OXXX.

   This is evaluated by the influence function in the following way: We
first assign territory under the assumption that X moves first in all
local positions in the original position;  then we reassing territory,
again under the assumption that `X' moves first in all local positions,
but after we let `O' make the move at `*'. These two territory
assignments are compared and the difference gives the territorial value
of the move.

   Technically, the assumption that `X' plays first everywhere is
implemented via an asymmetric pattern database in `barriers.db'.  What
exactly is a safe connection that stops hostile influence from passing
through is different for `O' and `X'; of course such a connection has
to be tighter for stones with color `O'. Also, additional intrusion
influence sources are added for `X' in places where `X' stones have
natural followup moves.

   In this specific example above, the asymmetry (before any move has
been made) would turn out as follows: If `X' is in turn to move, the
white influence would get stopped by a barrier at `*', leaving 4 points
of territory for `X'.  However, if `O' was next to move, then a
followup move for the white stones at the left would be assumed in the
form of an extra ("intrusion") influence source at `*'. This would get
stopped at `a', leaving three points of territory.

   Returning to the valuation of a move by `O' at `*', we get a value
of 1 for the move at `*'.  However, of course this move is sente once
it is worth playing, and should therefore (in miai counting) be awarded
an effective value of 2. Hence we need to recognize the followup value
of a move. GNU Go 3.0 took care of this by using patterns in
`patterns.db' that enforced an explicit followup value. Versions from
3.2 on instead compute a seperate followup influence to each move
considered. In the above example, an intrusion source will be added at
`a' as a followup move to `*'. This destroys all of Black's territory
and hence gives a followup value of 3.

   The pattern based followup value are still needed at some places,
however.

   To give another example, consider this position where we want to
estimate the value of an `O' move at `*':

     OOOXXX
     ..OX..
     ..OX..
     ...*..
     ------

   Before the move we assume `X' moves first in the local position (and
that `O' has to connect), which gives territory like this (lower case
letter identify territory for each player):

     OOOXXX
     ooOXxx
     o.OXxx
     o...xx
     ------

   Then we let `O' make the move at `*' and assume `X' moves first
again next.  The territory then becomes (`X' is also assumed to have to
connect):

     OOOXXX
     ooOXxx
     ooOX.x
     oo.O.x
     ------

   We see that this makes a difference in territory of 4, which is what
influence_delta_territory() should report. Then again, we have followup
value, and here also a reverse followup value. The reverse followup
value, which in this case will be so high that the move is treated as
reverse sente, is added by an explicit pattern. Other sources for
followup or reverse followup values are threats to capture a rescue a
string of stones.  See the code and comments in the function
`value_move_reaons' for how followup and reverse followup values are
used to adjust the effective move value.

   To give an example of territorial value where something is captured,
consider the `O' move at `*' here,

     XXXXXXXO
     X.OOOOXO
     X.O..O*O
     --------

   As before we first let the influence function determine territory
assuming X moves first, i.e. with a captured group:

     XXXXXXXO
     XxyyyyXO
     Xxyxxy.O
     --------

   Here `y' indicates `X' territory + captured stone, i.e. these count
for two points. After the `O' move at `*' we instead get

     XXXXXXXO
     X.OOOOXO
     X.OooOOO
     --------

   and we see that `X' has 16 territory fewer and `O' has two territory
more, for a total difference of 18 points.

   That the influence function counts the value of captured stones was
introduced in GNU Go 3.2. Previously this was instead done using the
effective_size heuristic. The effective size is the number of stones
plus the surrounding empty spaces which are closer to this string or
dragon than to any other stones. Here the `O' string would thus have
effective size 6 (number of stones) + 2 (interior eye) + 2*0.5 (the two
empty vertices to the left of the string, split half each with the
surrounding X string) + 1*0.33 (the connection point, split between
three strings) = 9.33. As noted this value was doubled, giving 18.67
which is reasonably close to the correct value of 18. The effective size
heuristic is still used in certain parts of the move valuation where we
can't easily get a more accurate value from the influence function (e.
g. attacks depending on a ko, attack threats).

   Note that this section only describes the territorial valuation of a
move.  Apart from that, GNU Go uses various heuristics in assigning a
strategical value (weakening and strengthening of other stones on the
board) to a move.  Also, the influence function isn't quite as well
tuned as the examples above may seem to claim. But it should give a
fairly good idea of how the design is intended.

   Another matter is that so far we have only considered the change in
secure territory. GNU Go 3.2 and later versions use a revised
heuristic, which is explained in the next section, to assign probable
territory to each player.

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File: gnugo.info,  Node: Territorial Details,  Next: The Influence Core,  Prev: Influence and Territory,  Up: Influence

13.5 Details of the Territory Valuation
=======================================

This section explains how GNU Go assigns a territorial value to an
intersection once the white and black influence have been computed.
The intention is that an intersection that has a chance of xx% of
becoming white territory is counted as 0.xx points of territory for
white, and similar for black.

   The algorithm in the function `new_value_territory' goes roughly as
follows:

   If `wi' is the white influence at a point, and `bi' the black
influence, then ` value = ( (wi-bi)/ (wi+bi) )^3' (positive values
indicates likley white territory, negative stand for black territory)
turns out to be very simple first guess that is still far off, but
reasonable enough to be useful.

   This value is then suspect a number of corrections. Assume that this
first guess resulted in a positive value.

   If both `bi' and `wi' are small, it gets reduced. What exactly is
"small" depends on whether the intersection is close to a corner or an
edge of the board, since it is easier to claim territory in the corner
than in the center.

   Then the value at each intersection is degraded to the minimum value
of its neighbors. This can be seen as a second implementation of the
proverb saying that there is no territory in the center of the board.
This step substantially reduces the size of spheres of territory that
are open at several sides.

   Finally, there are a number of patterns that explicitly forbid GNU
Go to count territory at some intersections. This is used e. g. for
false eyes that will eventually have to be filled in. Also, points for
prisoners are added.

   To fine tune this scheme, some revisions have been made to the
influence computations that are relevant for territorial evaluation.
This includes a reduced default attenuation and some revised pattern
handling.

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File: gnugo.info,  Node: The Influence Core,  Next: The Influence Algorithm,  Prev: Territorial Details,  Up: Influence

13.6 The Core of the Influence Function
=======================================

The basic influence radiation process can efficiently be implemented as
a breadth first search for adjacent and more distant points, using a
queue structure.

   Influence barriers can be found by pattern matching, assisted by
reading through constraints and/or helpers. Wall structures, invasion
points and intrusion points can be found by pattern matching as well.

   When influence is computed, the basic idea is that there are a number
of influence sources on the board, whose contributions are summed to
produce the influence values. For the time being we can assume that the
living stones on the board are the influence sources, although this is
not the whole story.

   The function `compute_influence()' contains a loop over the board,
and for each influence source on the board, the function
`accumulate_influence()' is called. This is the core of the influence
function. Before we get into the details, this is how the influence
field from a single isolated influence source of strength 100 turns out
(with an attenuation of 3.0):

       0  0  0  0  0  0  0  0  0  0  0
       0  0  0  0  1  1  1  0  0  0  0
       0  0  0  1  2  3  2  1  0  0  0
       0  0  1  3  5 11  5  3  1  0  0
       0  1  2  5 16 33 16  5  2  1  0
       0  1  3 11 33  X 33 11  3  1  0
       0  1  2  5 16 33 16  5  2  1  0
       0  0  1  3  5 11  5  3  1  0  0
       0  0  0  1  2  3  2  1  0  0  0
       0  0  0  0  1  1  1  0  0  0  0
       0  0  0  0  0  0  0  0  0  0  0

   These values are in reality floating point numbers but have been
rounded down to the nearest integer for presentation. This means that
the influence field does not stop when the numbers become zeroes.

   Internally `accumulate_influence()' starts at the influence source
and spreads influence outwards by means of a breadth first propagation,
implemented in the form of a queue. The order of propagation and the
condition that influence only is spread outwards guarantee that no
intersection is visited more than once and that the process terminates.
In the example above, the intersections are visited in the following
order:

       +  +  +  +  +  +  +  +  +  +  +
       + 78 68 66 64 63 65 67 69 79  +
       + 62 46 38 36 35 37 39 47 75  +
       + 60 34 22 16 15 17 23 43 73  +
       + 58 32 14  6  3  7 19 41 71  +
       + 56 30 12  2  0  4 18 40 70  +
       + 57 31 13  5  1  8 20 42 72  +
       + 59 33 21 10  9 11 24 44 74  +
       + 61 45 28 26 25 27 29 48 76  +
       + 77 54 52 50 49 51 53 55 80  +
       +  +  +  +  +  +  +  +  +  +  +

   The visitation of intersections continues in the same way on the
intersections marked '`+' and further outwards. In a real position
there will be stones and tight connections stopping the influence from
spreading to certain intersections. This will disrupt the diagram
above, but the main property of the propagation still remains, i.e. no
intersection is visited more than once and after being visited no more
influence will be propagated to the intersection.

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File: gnugo.info,  Node: The Influence Algorithm,  Next: Permeability,  Prev: The Influence Core,  Up: Influence

13.7 The Influence Algorithm
============================

Let `(m, n)' be the coordinates of the influence source and `(i, j)'
the coordinates of a an intersection being visited during propagation,
using the same notation as in the `accumulate_influence()' function.
Influence is now propagated to its eight closest neighbors, including
the diagonal ones, according to the follow scheme:

   For each of the eight directions `(di, dj)', do:

  1. Compute the scalar product `di*(i-m) + dj*(j-n)' between the
     vectors `(di,dj)' and `(i,j) - (m,n)'

  2. If this is negative or zero, the direction is not outwards and we
     continue with the next direction. The exception is when we are
     visiting the influence source, i.e. the first intersection, when
     we spread influence in all directions anyway.

  3. If `(i+di, j+dj)' is outside the board or occupied we also
     continue with the next direction.

  4. Let S be the strength of the influence at `(i, j)'. The influence
     propagated to `(i+di, j+dj)' from this intersection is given by
     `P*(1/A)*D*S', where the three different kinds of damping are:

        * The permeability `P', which is a property of the board
          intersections. Normally this is one, i.e. unrestricted
          propagation, but to stop propagation through e.g. one step
          jumps, the permeability is set to zero at such intersections
          through pattern matching. This is further discussed below.

        * The attenuation `A', which is a property of the influence
          source and different in different directions. By default this
          has the value 3 except diagonally where the number is twice
          as much. By modifying the attenuation value it is possible to
          obtain influence sources with a larger or a smaller effective
          range.

        * The directional damping `D', which is the squared cosine of
          the angle between `(di,dj)' and `(i,j) - (m,n)'. The idea is
          to stop influence from "bending" around an interfering stone
          and get a continuous behavior at the right angle cutoff. The
          choice of the squared cosine for this purpose is rather
          arbitrary, but has the advantage that it can be expressed as a
          rational function of `m', `n', `i', `j', `di', and `dj',
          without involving any trigonometric or square root
          computations. When we are visiting the influence source we
          let by convention this factor be one.

   Influence is typically contributed from up to three neighbors
"between" this intersection and the influence source. These values are
simply added together. As pointed out before, all contributions will
automatically have been made before the intersection itself is visited.

   When the total influence for the whole board is computed by
`compute_influence()', `accumulate_influence()' is called once for each
influence source. These invocations are totally independent and the
influence contributions from the different sources are added together.

\1f
File: gnugo.info,  Node: Permeability,  Next: Escape,  Prev: The Influence Algorithm,  Up: Influence

13.8 Permeability
=================

The permeability at the different points is initially one at all empty
intersections and zero at occupied intersections. To get a useful
influence function we need to modify this, however. Consider the
following position:

     |......
     |OOOO..
     |...O..
     |...a.X   ('a' empty intersection)
     |...O..
     |...OOO
     |.....O
     +------

   The corner is of course secure territory for `O' and clearly the `X'
stone has negligible effect inside this position. To stop `X' influence
from leaking into the corner we use pattern matching (pattern
Barrier1/Barrier2 in `barriers.db') to modify the permeability for `X'
at this intersection to zero. `O' can still spread influence through
this connection.

   Another case that needs to be mentioned is how the permeability
damping is computed for diagonal influence radiation. For horizontal
and vertical radiation we just use the permeability (for the relevant
color) at the intersection we are radiating from. In the diagonal case
we additionally multiply with the maximum permeability at the two
intersections we are trying to squeeze between. The reason for this can
be found in the diagram below:

     |...X    |...X
     |OO..    |Oda.
     |..O.    |.bc.
     |..O.    |..O.
     +----    +----

   We don't want `X' influence to be spread from `a' to `b', and since
the permeability at both c and d is zero, the rule above stops this.

\1f
File: gnugo.info,  Node: Escape,  Next: Break Ins,  Prev: Permeability,  Up: Influence

13.9 Escape
===========

One application of the influence code is in computing the
`dragon.escape_route' field. This is computed by the function
`compute_escape()' as follows.  First, every intersection is assigned
an escape value, ranging between 0 and 4, depending on the influence
value of the opposite color.

   The `escape_route' field is modified by the code in `surround.c'
(*note Surrounded Dragons::). It is divided by two for weakly surrounded
dragons, and set to zero for surrounded ones.

   In addition to assiging an escape value to empty vertices, we also
assign an escape value to friendly dragons. This value can range from 0
to 6 depending on the status of the dragon, with live dragons having
value 6.

   Then we sum the values of the resulting influence escape values over
the intersections (including friendly dragons) at distance 4, that is,
over those intersections which can be joined to the dragon by a path of
length 4 (and no shorter path) not passing adjacent to any unfriendly
dragon. In the following example, we sum the influence escape value
over the four vertices labelled '4'.


        . . . . . . . . .    . . . . . . . . .
        . . . . . X . . O    . . . . . X . . O
        . . X . . . . . O    . . X . 2 . 4 . O
        X . . . . . . . .    X . . 1 1 2 3 4 .
        X O . O . . . . O    X O 1 O 1 2 3 4 O
        X O . O . . . . .    X O 1 O 1 . 4 . .
        X O . . . X . O O    X O 1 . . X . . O
        . . . X . . . . .    . 1 . X . . . . .
        X . . . . X . . .    X . . . . X . . .
        . . . . . . . . .    . . . . . . . . .

   Since the dragon is trying to reach safety, the reader might wonder
why `compute_influence()' is called with the opposite color of the
dragon contemplating escape.  To explain this point, we first remind
the reader why there is a color parameter to `compute_influence()'.
Consider the following example position:

          ...XX...
          OOO..OOO
          O......O
          O......O
          --------

   Whether the bottom will become O territory depends on who is in turn
to play. This is implemented with the help of patterns in barriers.db,
so that X influence is allowed to leak into the bottom if X is in turn
to move but not if O is. There are also "invade" patterns which add
influence sources in sufficiently open parts of the board which are
handled differently depending on who is in turn to move.

   In order to decide the territorial value of an O move in the third
line gap above, influence is first computed in the original position
with the opponent (i.e. X) in turn to move. Then the O stone is played
to give:


          ...XX...
          OOO.OOOO
          O......O
          O......O
          --------

   Now influence is computed once more, also this time with X in turn to
move. The difference in territory (as computed from the influence
values) gives the territorial value of the move.

   Exactly how influence is computed for use in the escape route
estimation is all ad hoc. But it makes sense to assume the opponent
color in turn to move so that the escape possibilities aren't
overestimated. After we have made a move in the escape direction it is
after all the opponent's turn.

   The current escape route mechanism seems good enough to be useful
but is not completely reliable. Mostly it seems to err on the side of
being too optimistic.

\1f
File: gnugo.info,  Node: Break Ins,  Next: Surrounded Dragons,  Prev: Escape,  Up: Influence

13.10 Break Ins
===============

The code in `breakin.c' break-ins into territories that require deeper
tactical reading and are thus impossible to detect for the influence
module. It gets run after the influence module and revises its
territory valuations.

   The break-in code makes use of two public functions in
`readconnect.c',

   * int break_in(int str, const char goal[BOARDMAX], int *move) 

          Returns WIN if `str' can connect to the area `goal[]' (which
          may or may not contain stones), if the string's owner gets
          the first move.

   * int block_off(int str, const char goal[BOARDMAX], int *move) 

          Returns WIN if `str' cannot connect to the area `goal[]'
          (which may or may not contain stones), if the other color
          moves first.

   These functions are public front ends to their counterparts
`recursive_break_in' and `recursive_block_off', which call each other
recursively.

   The procedure is as follows: We look at all big (>= 10) territory
regions as detected by the influence code. Using the computation of
connection distances from readconnect.c, we compute all nearby vertices
of this territory. We look for the closest safe stones belonging to the
opponent.

   For each such string `str' we call

   * `break_in(str, territory)' if the opponent is assumed to be next
     to move,

   * `block_off(str, territory)' if the territory owner is next.

   If the break in is successful resp. the blocking unsuccessful, we
shrink the territory, and see whether the opponent can still break in.
We repeat this until the territory is shrunk so much that the opponent
can no longer reach it.

   To see the break in code in action run GNU Go on the file
`regression/games/break_in.sgf' with the option `-d0x102000'. Among the
traces you will find:

       Trying to break in from D7 to:
     E9 (1)  F9 (1)  G9 (1)  E8 (1)  F8 (1)  G8 (1)
     H8 (1)  G7 (1)  H7 (1)  J7 (1)  H6 (1)  J6 (1)
     H5 (1)  J5 (1)  H4 (1)  J4 (1)  H3 (1)  J3 (1)
     H2 (1)  J2 (1)
     block_off D7, result 0 PASS (355, 41952 nodes, 0.73 seconds)
     E9 (1)  F9 (1)  G9 (1)  E8 (1)  F8 (1)  G8 (1)
     H8 (1)  G7 (1)  H7 (1)  J7 (1)  H6 (1)  J6 (1)
     H5 (1)  J5 (1)  H4 (1)  J4 (1)  H3 (1)  J3 (1)
     H2 (1)  J2 (1)
     B:F4
       Erasing territory at E8 -b.
       Erasing territory at G3 -b.
       Now trying to break to smaller goal:
     F9 (1)  G9 (1)  F8 (1)  G8 (1)  H8 (1)  G7 (1)
     H7 (1)  J7 (1)  H6 (1)  J6 (1)  H5 (1)  J5 (1)
     H4 (1)  J4 (1)  H3 (1)  J3 (1)  H2 (1)  J2 (1)

   This means that the function `break_in' is called with the goal
marked 'a' in the following diagram. The code attempts to find out
whether it is possible to connect into this area from the string at
`D7'.

        A B C D E F G H J
      9 . . . . a a a . . 9
      8 . . . . a a a a . 8
      7 . . . X O O a a a 7
      6 . . . X X X O a a 6
      5 . . . . + . . a a 5
      4 . . . X . . O a a 4
      3 . . . . X . . a a 3
      2 . . . . . . O a a 2
      1 . . . . . . . . . 1
        A B C D E F G H J

   A breakin is found, so the goal is shrunk by removing `E9' and `J2',
then break_in is called again.

   In order to see what reading is actually done in order to do this
break in, you may load GNU Go in gtp mode, then issue the commands:

     loadsgf break_in.sgf
     = black

     start_sgftrace
     =

     break_in D7 E9 F9 G9 E8 F8 G8 H8 G7 H7 J7 H6 J6 H5 J5 H4 J4 H3 J3 H2 J2
     = 1 E8

     finish_sgftrace vars.sgf
     =

     start_sgftrace
     =

     break_in D7 F9 G9 F8 G8 H8 G7 H7 J7 H6 J6 H5 J5 H4 J4 H3 J3 H2 J2
     = 1 G7

     finish_sgftrace vars1.sgf

   This will produce two sgf files containing the variations caused by
these calls to the breakin code. The second file, `vars1.sgf' will
contain quite a few variations.

   The break in code makes a list of break ins which are found.  When
it is finished, the function `add_expand_territory_move' is called for
each break in, adding a move reason.

   The break in code is slow, and only changes a few moves by the engine
per game. Nevertheless we believe that it contributes substantially to
the strength of the program. The break in code is enabled by default in
GNU Go 3.6 at level 10, and disabled at level 9. In fact, this is the
*only* difference between levels 9 and 10 in GNU Go 3.6.

\1f
File: gnugo.info,  Node: Surrounded Dragons,  Next: Influential Patterns,  Prev: Break Ins,  Up: Influence

13.11 Surrounded Dragons
========================

When is a dragon surrounded?

   As has been pointed out by Bruce Wilcox, the geometric lines
connecting groups of the opposite color are often important. It is very
hard to prevent the escape of this `O' dragon:

     ..........
     .....O....
     .X.......X
     .X...O...X
     ..........
     ..........
     ----------

   On the other hand, this dragon is in grave danger:

     ..........
     ..........
     .X.......X
     .....O....
     .X.......X
     .X...O...X
     ..........
     ..........
     ----------

   The difference between these two positions is that in the first, the
`O' dragon crosses the line connecting the top two `X' stones.

   Code in `surround.c' implements a test for when a dragon is
surrounded.  The idea is to compute the convex hull of the _surround
set_, that is, the set stones belonging to unfriendly neighbor dragons.
If the dragon is contained within that hull. If it is, it is said to be
_surrounded_.

   In practice this scheme is modified slightly. The implementation
uses various algorithms to compute distances and hostile stones are
discarded from the surround set when a pair other hostile ones can be
found which makes the considered one useless. For example, in the
following position the bottom `O' stone would get discarded.

     O.X.O
     .....
     .O.O.
     .....
     ..O..

   Also, points are added to the surround set below stones on the
second and third lines. This should account for the edge being a
natural barrier.

   In order to compute distances between corners of the convex hull a
sorting by angle algorithm has been implemented. If the distance
between a pair enclosing stones is large, the surround status gets
decreased to `WEAKLY_SURROUNDED', or even 0 for very large ones.

   The sorting by angle must be explained. A small diagram will
probably help :

     .O.O.
     O...O
     ..X..
     O...O
     .O.O.

   The sorting algorithm will generate this:

     .4.5.
     3...6
     ..X..
     2...7
     .1.8.

   That is, the points are sorted by ascending order of the measure of
the angle S-G-O, where S is SOUTH, G the (approximated) gravity center
of the goal, and O the position of the considered hostile stones.

   The necessity of such sorting appears when one tries to measure
distances between enclosing stones without sorting them, just by using
directly the existing left and right corners arrays. In some positions,
the results will be inconsistent. Imagine, for example a position where
for instance the points 1,2,3,4,6 and 7 were in the left arrary,
leaving only 5 and 8 in the right array. Because of the large distance
between 5 and 8, the dragon would have declared weak surrounded or not
surrounded at all. Such cases are rare but frequent enough to require
the angle sorting.

   The following position:

     O.X.O
     .....
     .O.O.

   This is "more" surrounded than the following position:

     O.XXXXXX.O
     ..........
     .O......O.

   In the second case, the surround status would be lowered to
`WEAKLY_SURROUNDED'.

   The surround code is used to modify the escape_route field in the
dragon2 data array. When a dragon is WEAKLY_SURROUNDED, the
escape_route is divided by 2. If the dragon is SURROUNDED, escape_route
is simply set to 0.

\1f
File: gnugo.info,  Node: Influential Patterns,  Next: Influential Display,  Prev: Surrounded Dragons,  Up: Influence

13.12 Patterns used by the Influence module
===========================================

This section explains the details of the pattern databases used for the
influence computation.

   First, we have the patterns in `influence.db', which get matched
symmetrically for both colors.

   * `E'

          These patterns add extra influence sources close to some
          shapes like walls.  This tries to reflect their extra
          strength. These patterns are not used in the influence
          computations relevant for territory valuations, but they are
          useful for getting a better estimate of strengths of groups.

   * `I'

          These patterns add extra influence sources at typical
          invasion points.  Usually they are of small strength. If they
          additionally have the class `s', the extra influence source
          is added for both colors. Otherwise, only the player assumed
          to be next to move gets the benefit.

   The patterns in `barriers.db' get matched only for `O' being the
player next to move.

   * `A'

          Connections between `X' stones that stop influence of `O'.
          They have to be tight enough that `O' cannot break through,
          even though he is allowed to move first.

   * `D'

          Connections between `O' stones that stop influence of `X'. The
          stones involved can be more loosely connected than those in
          `A' patterns.

   * `B'

          These indicate positions of followup moves for the `O' stone
          marked with `Q' in the pattern. They are used to reduce the
          territory e. g.  where a monkey jump is possible. Also, they
          are used in the computation of the followup influence, if the
          `Q' stone was the move played (or a stone saved by the move
          played).

   * `t'

          These patterns indicate intersections where one color will
          not be able to get territory, for example in a false eye. The
          points are set with a call to the helper non_oterritory or
          non_xterritory in the action of the pattern.

   The intrusion patterns (`B') are more powerful than the description
above might suggest. They can be very helpful in identifying weak shapes
(by adding an intrusion source for the opponent where he can break
through).  A negative inference for this is that a single bad `B'
pattern, e. g.  one that has a wrong constraint, typically causes 5 to
10 `FAIL's in the regression test suite.

   Influence Patterns can have autohelper constraints as usual. As for
the constraint attributes, there are (additionally to the usual ones
`O', `o', `X' and `x'), attributes `Y' and `FY'. A pattern marked with
`Y' will only be used in the influence computations relevant for the
territory valuation, while `FY' patterns only get used in the other
influence computations.

   The action of an influence pattern is at the moment only used for
non-territory patterns as mentioned above, and as a workaround for a
problem with `B' patterns in the followup influence.

   To see why this workaround is necessary, consider the follwoing
situation:


     ..XXX
     .a*.O
     .X.O.
     ..XXO

   (Imagine that there is `X' territory on the left.)

   The move by `O' at `*' has a natural followup move at `a'.  So, in
the computation of the followup influence for `*', there would be an
extra influence source for `O' at `a' which would destroy a lot of
black territory on the left. This would give a big followup value, and
in effect the move `*' would be treated as sente.

   But of course it is gote, since `X' will answer at `a', which both
stops the possible intrusion and  threatens to capture `*'. This
situation is in fact quite common.

   Hence we need an additional constraint that can tell when an
intrusion pattern can be used in followup influence. This is done by
misusing the action line: An additional line

     >return <condition>;

   gets added to the pattern. The `condition' should be true if the
intrusion cannot be stopped in sente. In the above example, the relevant
intrusion pattern will have an action line of the form

     >return (!xplay_attack(a,b));

   where `b' refers to the stone at `*'. In fact, almost all
followup-specific constraints look similar to this.

\1f
File: gnugo.info,  Node: Influential Display,  Next: Influence Tuning,  Prev: Influential Patterns,  Up: Influence

13.13 Colored display and debugging of influence
================================================

There are various ways to obtain detailed information about the
influence computations. Colored diagrams showing influence are possible
from a colored xterm or rxvt window.

   There are two options controlling when to generate diagrams:

   * `-m 0x08' or `-m 8'

          Show diagrams for the initial influence computation. This is
          done twice, the first time before `make_dragons()' is run and
          the second time after. The difference is that dead dragons
          are taken into account the second time. Tactically captured
          worms are taken into account both times.

   * `--debug-influence LOCATION'

          Show influence diagrams after the move at the given location.
          An important limitation of this option is that it's only
          effective for moves that the move generation is considering.

   The other options control which diagrams should be generated in these
situations. You have to specify at least one of the options above and
at least one of the options below to generate any output.

   * The options below must be combined with one of the two previous
ones, or the diagram will not be printed. For example to print the
influence diagram, you may combine 0x08 and 0x010, and use the option
`-m 0x018'.*

   * `-m 0x010' or `-m 16'

          Show colored display of territory/moyo/area regions.
             - territory: cyan

             - moyo: yellow

             - area: red
          This feature is very useful to get an immediate impression of
          the influence regions as GNU Go sees them.

   * `-m 0x20' or `-m 32'

          Show numerical influence values for white and black. These
          come in two separate diagrams, the first one for white, the
          second one for black. Notice that the influence values are
          represented by floats and thus have been rounded in these
          diagrams.

   * `-m 0x40' or `-m 64'

          This generates two diagrams showing the permeability for
          black and white influence on the board.

   * `-m 0x80' or `-m 128'

          This shows the strength of the influence sources for black
          and white across the board. You will see sources at each
          lively stone (with strength depending on the strength of this
          stone), and sources contributed by patterns.

   * `-m 0x100' or `-m 256'

          This shows the attenuation with which the influence sources
          spread influence across the board. Low attenuation indicates
          far-reaching influence sources.

   * `-m 0x200' or `-m 512'

          This shows the territory valuation of GNU Go. Each
          intersection is shown with a value between -1.0 and +1.0 (or
          -2 resp. +2 if there is a dead stone on this intersection).
          Positive values indicate territory for white. A value of -0.5
          thus indicates a point where black has a 50% chance of
          getting territory.

   Finally, there is the debug option `-d 0x1' which turns on on
`DEBUG_INFLUENCE'. This gives a message for each influence pattern that
gets matched. Unfortunately, these are way too many messages making it
tedious to navigate the output. However, if you discover an influence
source with `-m 0x80' that looks wrong, the debug output can help you
to quickly find out the responsible pattern.

\1f
File: gnugo.info,  Node: Influence Tuning,  Prev: Influential Display,  Up: Influence

13.14 Influence Tuning with `view.pike'
=======================================

A useful program in the regression directory is `view.pike'.  To run
it, you need Pike, which you may download from
`http://pike.ida.liu.se/'.

   The test case `endgame:920' fails in GNU Go 3.6. We will explain how
to fix it.

   Start by firing up view.pike on testcase endgame:920, e.g. by running
`pike view.pike endgame:920' in the regression directory.

   We see from the first view of move values that filling dame at P15 is
valued highest with 0.17 points while the correct move at C4 is valued
slightly lower with 0.16. The real problem is of course that C4 is
worth a full point and thus should be valued about 1.0.

   Now click on C4 to get a list of move reasons and move valuation
information. Everything looks okay except that change in territory is
0.00 rather than 1.00 as it ought to be.

   We can confirm this by choosing the "delta territory for..." button
and again clicking C4. Now B5 should have been marked as one point of
change in territory, but it's not.

   Next step is to enter the influence debug tool. Press the "influence"
button, followed by "black influence, dragons known," and "territory
value." This shows the expected territory if black locally moves first
everywhere (thus "black influence"). Here we can see that B5 is
incorrectly considered as 1.0 points of white territory.

   We can compare this with the territory after a white move at C4
(still assuming that black locally moves first everywhere after that) by
pressing "after move influence for..." and clicking C4. This looks
identical, as expected since delta territory was 0, but here it is
correct that B5 is 1.0 points of territory for white.

   The most straightforward solution to this problem is to add a
non-territory pattern, saying that white can't get territory on B5 if
black moves first. The nonterritory patterns are in `barriers.db'.

     Pattern Nonterritory56

     ...
     X.O
     ?O.

     :8,t

     eac
     XbO
     ?Od

     ;oplay_attack(a,b,c,d,d)

     >non_xterritory(e);

   In these patterns it's always assumed that `O' moves first and thus
it says that `X' can't get territory at `B5' (`e' in the pattern). Now
we need to be a bit careful however since after `O' plays at `a' and
`X' cuts in at `b', it may well happen that `O' needs to defend around
`d', allowing `X' to cut at `c', possibly making the nonterritory
assumption invalid. It's difficult to do this entirely accurate, but
the constraint above is fairly conservative and should guarantee that
`a' is safe in most, although not all, cases.

\1f
File: gnugo.info,  Node: Monte Carlo Go,  Next: Libboard,  Prev: Influence,  Up: Top

14 Monte Carlo Go
*****************

In Monte Carlo Go the engine plays random games to the end, generating
moves from a pattern database within the context of the algorithm UCT
(upper confidence bounds applied to trees).  This algorithm allowed the
program MoGo (`http://www.lri.fr/~gelly/MoGo.htm', to become the first
computer program to defeat a professional while taking a 9 stone
handicap (`http://senseis.xmp.net/?MoGo').

   GNU Go 3.8 can play 9x9 Go with the option `--monte-carlo' using the
UCT algorithm.  For command line options, see *Note Invoking GNU Go::.

   During reading, the engine makes incremental updates of local 3x3
neighborhood, suicide status, self-atari status, and number of stones
captured, for each move.

   GNU Go's simulations (Monte Carlo games) are pattern generated.  The
random playout move generation is distributed strictly proportional to
move values computed by table lookup from a local context consisting of
3x3 neighborhood, opponent suicide status, own and opponent self-atari
status, number of stones captured by own and opponent move, and
closeness to the previous move. Let's call this local context simply "a
pattern" and the table "pattern values" or simply "patterns".

   There are three built-in databases that you can select using the
option `--mc-patterns <name>', where `<name>' is one of

   * `mc_montegnu_classic'

   * `mc_mogo_classic'

   * `mc_uniform'

   The first of these is an approximation of the previous random move
generation algorithm. The `mogo_classic' pattern values is an
approximation of the simulation policy used by early versions of MoGo,
as published in the report odification of UCT with Patterns in
Monte-Carlo Go (http://hal.inria.fr/inria-00117266) RR-6062, by Sylvain
Gelly, Yizao Wang, Rémi Munos, and Olivier Teytaud. The uniform pattern
values is the so called "light" playout which chooses uniformly between
all legal moves except single point proper eyes.

   If you're not satisfied with these you can also tune your own
pattern values with a pattern database file and load it at runtime with
`--mc-load-patterns <name>' adding your own pattern database.

   Let's start with the uniform pattern values. Those are defined by the
file `patterns/mc_uniform.db', which looks like this:


     oOo
     O*O
     oO?

     :0

     oOo
     O*O
     ---

     :0

     |Oo
     |*O
     +--

     :0

   Patterns are always exactly 3x3 in size with the move at the center
point. The symbols are the usual for GNU Go pattern databases:

     * move
     O own stone (i.e. the same color as the color to move)
     o own stone or empty
     X opponent stone
     x opponent stone or empty
     ? own stone, opponent stone, or empty
     | vertical edge
     - horizontal edge
     + corner

   There's also a new symbol:

     % own stone, opponent stone, empty, or edge

   After the pattern comes a line starting with a colon. In all these
patterns it says that the pattern has a move value of 0, i.e. must not
be played. Unmatched patterns have a default value of 1. When all move
values are zero for both players, the playout will stop. Including the
three patterns above is important because otherwise the playouts would
be likely to go on indefinitely, or as it actually happens be
terminated at a hard-coded limit of 600 moves. Also place these
patterns at the top of the database because when multiple patterns
match, the first one is used, regardless of the values.

   When using only these patterns you will probably notice that it plays
rather heavy, trying hard to be solidly connected. This is because
uniform playouts are badly biased with a high probability of non-solid
connections being cut apart. To counter this you could try a pattern
like

     ?X?
     O*O
     x.?

     :20,near

   to increase the probability that the one-point jump is reinforced
when threatened. Here we added the property "near", which means that the
pattern only applies if the previous move was played "near" this move.
Primarily "near" means within the surrounding 3x3 neighborhood but it
also includes certain cases of liberties of low-liberty strings
adjacent to the previous move, e.g. the move to extend out of an atari
created by the previous move. You have to read the source to find out
the exact rules for nearness.

   We could also be even more specific and say

     ?X?
     O*O
     x.?

     :20,near,osafe,xsafe

   to exclude the cases where this move is a self atari (osafe) or would
be a self-atari for the opponent (xsafe).

   It may also be interesting to see the effect of capturing stones. A
catch-all pattern for captures would be

     ?X%
     ?*%
     %%%

     :10,ocap1,osafe
     :20,ocap2
     :30,ocap3

   where we have used multiple colon lines to specify different move
values depending on the number of captured stones; value 10 for a
single captured stone, value 20 for two captured stones, and value 30
for three or more captured stones. Here we also excluded self-atari
moves in the case of 1 captured stone in order to avoid getting stuck
in triple-ko in the playouts (there's no superko detection in the
playouts).

   The full set of pattern properties is as follows:

`near'
     The move is "near" the previous move.

`far'
     The move is not "near" the previous move.

`osafe'
     The move is not a self-atari.

`ounsafe'
     The move is a self-atari.

`xsafe'
     The move would not be a self-atari for the opponent.

`xunsafe'
     The move would be a self-atari for the opponent.

`xsuicide'
     The move would be suicide for the opponent

`xnosuicide'
     The move would not be suicide for the opponent.

`ocap0'
     The move captures zero stones.

`ocap1'
     The move captures one stone.

`ocap2'
     The move captures two stones.

`ocap3'
     The move captures three or more stones.

`ocap1+'
     The move captures one or more stones.

`ocap1-'
     The move captures at most one stone.

`ocap2+'
     The move captures two or more stones.

`ocap2-'
     The move captures at most two stones.

`xcap0'
     An opponent move would capture zero stones.

`xcap1'
     An opponent move would capture one stone.

`xcap2'
     An opponent move would capture two stones.

`xcap3'
     An opponent move would capture three or more stones.

`xcap1+'
     An opponent move would capture one or more stones.

`xcap1-'
     An opponent move would capture at most one stone.

`xcap2+'
     An opponent move would capture two or more stones.

`xcap2-'
     An opponent move would capture at most two stones.

   These can be combined arbitrarily but all must be satisfied for the
pattern to take effect. If contradictory properties are combined, the
pattern will never match.

14.0.1 Final Remarks
--------------------

   * Move values are unsigned 32-bit integers. To avoid overflow in
     computations it is highly recommended to keep the values below
     10000000 or so.

   * There is no speed penalty for having lots of patterns in the
     database. The average time per move is approximately constant
     (slightly dependent on how often stones are captured or become low
     on liberties) and the time per game mostly depends on the average
     game length.

   * For more complex pattern databases, see
     `patterns/mc_montegnu_classic.db' and
     `patterns/mc_mogo_classic.db'.

   Nobody really knows how to tune the random playouts to get as strong
engine as possible. Please play with this and report any interesting
findings, especially if you're able to make it substantially stronger
than the `montegnu_classic' patterns.

\1f
File: gnugo.info,  Node: Libboard,  Next: SGF,  Prev: Monte Carlo Go,  Up: Top

15 The Board Library
********************

* Menu:

* Board Data Structures::      Board Data Structures
* The Board Array::	       One-dimensional board array
* Incremental Board::	  	Incremental board data structures
* Some Board Functions::      	Explanation of some board functions

   The foundation of the GNU Go engine is a library of very efficient
routines for handling go boards.  This board library, called
`libboard', can be used for those programs that only need a basic go
board but no AI capability. One such program is `patterns/joseki.c',
which compiles joseki pattern databases from SGF files.

   If you want to use the board library in your own program, you need
all the .c-files listed under libboard_SOURCES in engine/Makefile.am,
and the files in the directories sgf/ and utils/. Then you should
include engine/board.h in your code.

   The library consists of the following files:

   * `board.h'

          The public interface to the board library.

   * `board.c'

          The basic board code. It uses incremental algorithms for
          keeping track of strings and liberties on the go board.

   * `boardlib.c'

          This contains all global variable of the board library.

   * `hash.c'

          Code for hashing go positions.

   * `sgffile.c'

          Implementation of output file in SGF format.

   * `printutils.c'

          Utilities for printing go boards and other things.


   To use the board library, you must include `liberty.h' just like
when you use the whole engine, but of course you cannot use all the
functions declared in it, i.e. the functions that are part of the
engine, but not part of the board library.  You must link your
application with `libboard.a'.

\1f
File: gnugo.info,  Node: Board Data Structures,  Next: The Board Array,  Up: Libboard

15.1 Board Data structures
==========================

The basic data structures of the board correspond tightly to the
`board_state' struct described in *Note The Board State::. They are all
stored in global variables for efficiency reasons, the most important
of which are:


     int           board_size;
     Intersection  board[MAXSIZE];
     int           board_ko_pos;

     float         komi;
     int           white_captured;
     int           black_captured;

     Hash_data     hashdata;

   The description of the `Position' struct is applicable to these
variables also, so we won't duplicate it here.  All these variables are
globals for performance reasons.  Behind these variables, there are a
number of other private data structures.  These implement incremental
handling of strings, liberties and other properties (*note Incremental
Board::). The variable `hashdata' contains information about the hash
value for the current position (*note Hashing::).

   These variables should never be manipulated directly, since they are
only the front end for the incremental machinery. They can be read, but
should only be written by using the functions described in the next
section. If you write directly to them, the incremental data structures
will become out of sync with each other, and a crash is the likely
result.

\1f
File: gnugo.info,  Node: The Board Array,  Next: Incremental Board,  Prev: Board Data Structures,  Up: Libboard

15.2 The Board Array
====================

GNU Go represents the board in a one-dimensional array called `board'.
For some purposes a two dimensional indexing of the board by parameters
`(i,j)' might be used.

   The `board' array includes out-of-board markers around the board. To
make the relation to the old two-dimensional board representation
clear, this figure shows how the 1D indices correspond to the 2D
indices when MAX_BOARD is 7.

       j  -1   0   1   2   3   4   5   6
     i +----------------------------------
     -1|   0   1   2   3   4   5   6   7
      0|   8   9  10  11  12  13  14  15
      1|  16  17  18  19  20  21  22  23
      2|  24  25  26  27  28  29  30  31
      3|  32  33  34  35  36  37  38  39
      4|  40  41  42  43  44  45  46  47
      5|  48  49  50  51  52  53  54  55
      6|  56  57  58  59  60  61  62  63
      7|  64  65  66  67  68  69  70  71  72

   To convert between a 1D index `pos' and a 2D index `(i,j)', the
macros `POS', `I', and `J' are provided, defined as below:

     #define POS(i, j)    ((MAX_BOARD + 2) + (i) * (MAX_BOARD + 1) + (j))
     #define I(pos)       ((pos) / (MAX_BOARD + 1) - 1)
     #define J(pos)       ((pos) % (MAX_BOARD + 1) - 1)

   All 1D indices not corresponding to points on the board have the out
of board marker value `GRAY'. Thus if `board_size' and `MAX_BOARD' both
are 7, this looks like

       j  -1   0   1   2   3   4   5   6
     i +----------------------------------
     -1|   #   #   #   #   #   #   #   #
      0|   #   .   .   .   .   .   .   .
      1|   #   .   .   .   .   .   .   .
      2|   #   .   .   .   .   .   .   .
      3|   #   .   .   .   .   .   .   .
      4|   #   .   .   .   .   .   .   .
      5|   #   .   .   .   .   .   .   .
      6|   #   .   .   .   .   .   .   .
      7|   #   #   #   #   #   #   #   #   #

   The indices marked `#' have value `GRAY'.  If `MAX_BOARD' is 7 and
`board_size' is only 5:

       j  -1   0   1   2   3   4   5   6
     i +----------------------------------
     -1|   #   #   #   #   #   #   #   #
      0|   #   .   .   .   .   .   #   #
      1|   #   .   .   .   .   .   #   #
      2|   #   .   .   .   .   .   #   #
      3|   #   .   .   .   .   .   #   #
      4|   #   .   .   .   .   .   #   #
      5|   #   #   #   #   #   #   #   #
      6|   #   #   #   #   #   #   #   #
      7|   #   #   #   #   #   #   #   #   #

   Navigation on the board is done by the `SOUTH', `WEST', `NORTH', and
`EAST' macros,

     #define NS           (MAX_BOARD + 1)
     #define WE           1
     #define SOUTH(pos)   ((pos) + NS)
     #define WEST(pos)    ((pos) - 1)
     #define NORTH(pos)   ((pos) - NS)
     #define EAST(pos)    ((pos) + 1)

   There are also shorthand macros `SW', `NW', `NE', `SE', `SS', `WW',
`NN', `EE' for two step movements.

   Any movement from a point on the board to an adjacent or diagonal
vertex is guaranteed to produce a valid index into the board array, and
the color found is GRAY if it is not on the board. To do explicit tests
for out of board there are two macros

     #define ON_BOARD(pos) (board[pos] != GRAY)
     #define ON_BOARD1(pos) (((unsigned) (pos) < BOARDSIZE) && board[pos] != GRAY)

   where the first one should be used in the algorithms and the second
one is useful for assertion tests.

   The advantage of a one-dimensional board array is that it gives a
significant performance advantage. We need only one variable to
determine a board position, which means that many functions need less
arguments. Also, often one computation is sufficient for 1D-coordinate
where we would need two with two 2D-coordinates: If we, for example,
want to have the coordinate of the upper right of `pos', we can do this
with `NORTH(EAST(pos))' instead of `(i+1, j-1)'.

   *Important*: The 2D coordinate `(-1,-1)', which is used for pass and
sometimes to indicate no point, maps to the 1D coordinate `0', not to
`-1'. Instead of a plain `0', use one of the macros `NO_MOVE' or
`PASS_MOVE'.

   A loop over multiple directions is straightforwardly written:

       for (k = 0; k < 4; k++) {
         int d = delta[k];
         do_something(pos + d);
       }

   The following constants are useful for loops over the entire board
and allocation of arrays with a 1-1 mapping to the board.

     #define BOARDSIZE    ((MAX_BOARD + 2) * (MAX_BOARD + 1) + 1)
     #define BOARDMIN     (MAX_BOARD + 2)
     #define BOARDMAX     (MAX_BOARD + 1) * (MAX_BOARD + 1)

   `BOARDSIZE' is the actual size of the 1D board array, `BOARDMIN' is
the first index corresponding to a point on the board, and `BOARDMAX'
is one larger than the last index corresponding to a point on the board.

   Often one wants to traverse the board, carrying out some function at
every vertex. Here are two possible ways of doing this:

       int m, n;
       for (m = 0; m < board_size; m++)
         for (n = 0; n < board_size; n++) {
           do_something(POS(m, n));
         }

   Or:

       int pos;
       for (pos = BOARDMIN; pos < BOARDMAX; pos++) {
         if (ON_BOARD(pos))
           do_something(pos);
       }

\1f
File: gnugo.info,  Node: Incremental Board,  Next: Some Board Functions,  Prev: The Board Array,  Up: Libboard

15.3 Incremental Board data structures
======================================

In addition to the global board state, the algorithms in `board.c'
implement a method of incremental updates that keeps track of the
following information for each string:

   * The color of the string.

   * Number of stones in the string.

   * Origin of the string, i.e. a canonical reference point, defined to
     be the stone with smallest 1D board coordinate.

   * A list of the stones in the string.

   * Number of liberties.

   * A list of the liberties. If there are too many liberties the list
     is truncated.

   * The number of neighbor strings.

   * A list of the neighbor strings.

   The basic data structure is

     struct string_data {
       int color;                       /* Color of string, BLACK or WHITE */
       int size;                        /* Number of stones in string. */
       int origin;                      /* Coordinates of "origin", i.e. */
                                        /* "upper left" stone. */
       int liberties;                   /* Number of liberties. */
       int libs[MAX_LIBERTIES];         /* Coordinates of liberties. */
       int neighbors;                   /* Number of neighbor strings */
       int neighborlist[MAXCHAIN];      /* List of neighbor string numbers. */
       int mark;                        /* General purpose mark. */
     };

     struct string_data string[MAX_STRINGS];

   It should be clear that almost all information is stored in the
`string' array. To get a mapping from the board coordinates to the
`string' array we have

     static int string_number[BOARDMAX];

which contains indices into the `string' array. This information is only
valid at nonempty vertices, however, so it is necessary to first verify
that `board[pos] != EMPTY'.

   The `string_data' structure does not include an array of the stone
coordinates. This information is stored in a separate array:

     static int next_stone[BOARDMAX];

   This array implements cyclic linked lists of stones. Each vertex
contains a pointer to another (possibly the same) vertex. Starting at
an arbitrary stone on the board, following these pointers should
traverse the entire string in an arbitrary order before coming back to
the starting point. As for the 'string_number' array, this information
is invalid at empty points on the board. This data structure has the
good properties of requiring fixed space (regardless of the number of
strings) and making it easy to add a new stone or join two strings.

   Additionally the code makes use of some work variables:

     static int ml[BOARDMAX];
     static int liberty_mark;
     static int string_mark;
     static int next_string;
     static int strings_initialized = 0;

   The `ml' array and `liberty_mark' are used to "mark" liberties on
the board, e.g. to avoid counting the same liberty twice. The
convention is that if `ml[pos]' has the same value as `liberty_mark',
then `pos' is marked. To clear all marks it suffices to increase the
value of `liberty_mark', since it is never allowed to decrease.

   The same relation holds between the `mark' field of the `string_data'
structure and `string_mark'. Of course these are used for marking
individual strings.

   `next_string' gives the number of the next available entry in the
`string' array. Then `strings_initialized' is set to one when all data
structures are known to be up to date. Given an arbitrary board
position in the `board' array, this is done by calling
`incremental_board_init()'. It is not necessary to call this function
explicitly since any other function that needs the information does
this if it has not been done.

   The interesting part of the code is the incremental update of the
data structures when a stone is played and subsequently removed. To
understand the strategies involved in adding a stone it is necessary to
first know how undoing a move works. The idea is that as soon as some
piece of information is about to be changed, the old value is pushed
onto a stack which stores the value and its address. The stack is built
from the following structures:

     struct change_stack_entry {
       int *address;
       int value;
     };

     struct change_stack_entry change_stack[STACK_SIZE];
     int change_stack_index;

and manipulated with the macros

     BEGIN_CHANGE_RECORD()
     PUSH_VALUE(v)
     POP_MOVE()

   Calling `BEGIN_CHANGE_RECORD()' stores a null pointer in the address
field to indicate the start of changes for a new move. As mentioned
earlier `PUSH_VALUE()' stores a value and its corresponding address.
Assuming that all changed information has been duly pushed onto the
stack, undoing the move is only a matter of calling `POP_MOVE()', which
simply assigns the values to the addresses in the reverse order until
the null pointer is reached. This description is slightly simplified
because this stack can only store 'int' values and we need to also
store changes to the board. Thus we have two parallel stacks where one
stores `int' values and the other one stores `Intersection' values.

   When a new stone is played on the board, first captured opponent
strings, if any, are removed. In this step we have to push the board
values and the `next_stone' pointers for the removed stones, and update
the liberties and neighbor lists for the neighbors of the removed
strings. We do not have to push all information in the 'string' entries
of the removed strings however. As we do not reuse the entries they
will remain intact until the move is pushed and they are back in use.

   After this we put down the new stone and get three distinct cases:

  1. The new stone is isolated, i.e. it has no friendly neighbor.

  2. The new stone has exactly one friendly neighbor.

  3. The new stone has at least two friendly neighbors.

   The first case is easiest. Then we create a new string by using the
number given by `next_string' and increasing this variable. The string
will have size one, `next_stone' points directly back on itself, the
liberties can be found by looking for empty points in the four
directions, possible neighbor strings are found in the same way, and
those need also to remove one liberty and add one neighbor.

   In the second case we do not create a new string but extend the
neighbor with the new stone. This involves linking the new stone into
the cyclic chain, if needed moving the origin, and updating liberties
and neighbors. Liberty and neighbor information also needs updating for
the neighbors of the new stone.

   In the third case finally, we need to join already existing strings.
In order not to have to store excessive amounts of information, we
create a new string for the new stone and let it assimilate the
neighbor strings. Thus all information about those can simply be left
around in the 'string' array, exactly as for removed strings. Here it
becomes a little more complex to keep track of liberties and neighbors
since those may have been shared by more than one of the joined
strings. Making good use of marks it all becomes rather straightforward
anyway.

   The often used construction

         pos = FIRST_STONE(s);
         do {
             ...
             pos = NEXT_STONE(pos);
         } while (!BACK_TO_FIRST_STONE(s, pos));

traverses the stones of the string with number `s' exactly once, with
`pos' holding the coordinates. In general `pos' is used as board
coordinate and `s' as an index into the `string' array or sometimes a
pointer to an entry in the `string' array.

\1f
File: gnugo.info,  Node: Some Board Functions,  Prev: Incremental Board,  Up: Libboard

15.4 Some Board Functions
=========================

*Reading*, often called *search* in computer game theory, is a
fundamental process in GNU Go. This is the process of generating
hypothetical future boards in order to determine the answer to some
question, for example "can these stones live."  Since these are
hypothetical future positions, it is important to be able to undo them,
ultimately returning to the present board. Thus a move stack is
maintained during reading. When a move is tried, by the function
`trymove', or its variant `tryko'. This function pushes the current
board on the stack and plays a move. The stack pointer `stackp', which
keeps track of the position, is incremented. The function `popgo()'
pops the move stack, decrementing `stackp' and undoing the last move
made.

   Every successful `trymove()' must be matched with a `popgo()'.  Thus
the correct way of using this function is:


       if (trymove(pos, color, ... )) {
            ...    [potentially lots of code here]
            popgo();
       }

In case the move is a ko capture, the legality of the capture is
subject to the komaster scheme (*note Ko::).

   * `int trymove(int pos, int color, const char *message)' 

          Returns true if `(pos)' is a legal move for `color'. In that
          case, it pushes the board on the stack and makes the move,
          incrementing `stackp'. If the reading code is recording
          reading variations (as with `--decide-string' or with `-o'),
          the string `*message' will be inserted in the SGF file as a
          comment. The comment will also refer to the string at `str'
          if this is not `0'. The value of `str' can be NO_MOVE if it
          is not needed but otherwise the location of `str' is included
          in the comment.

   * `int tryko(int pos, int color, const char *message)' 

          `tryko()' pushes the position onto the stack, and makes a move
          `pos' of `color'. The move is allowed even if it is an
          illegal ko capture. It is to be imagined that `color' has
          made an intervening ko threat which was answered and now the
          continuation is to be explored. Return 1 if the move is legal
          with the above caveat. Returns zero if it is not legal
          because of suicide.

   * `void popgo()' 

          Pops the move stack. This function must (eventually) be
          called after a succesful `trymove' or `tryko' to restore the
          board position. It undoes all the changes done by the call to
          `trymove/tryko' and leaves the board in the same state as it
          was before the call.

          *NOTE*: If `trymove/tryko' returns `0', i.e. the tried move
          was not legal, you must *not* call `popgo'.

   * `int komaster_trymove(int pos, int color, const char *message, int
     str, int *is_conditional_ko, int consider_conditional_ko)' 

          Variation of `trymove'/`tryko' where ko captures (both
          conditional and unconditional) must follow a komaster scheme
          (*note Ko::).


   As you see, `trymove()' plays a move which can be easily retracted
(with `popgo()') and it is call thousands of times per actual game move
as GNU Go analyzes the board position.  By contrast the function
`play_move()' plays a move which is intended to be permanent, though it
is still possible to undo it if, for example, the opponent retracts a
move.

   * `void play_move(int pos, int color)' 

          Play a move. If you want to test for legality you should
          first call `is_legal()'. This function strictly follows the
          algorithm:
            1. Place a stone of given color on the board.

            2. If there are any adjacent opponent strings without
               liberties, remove them and increase the prisoner count.

            3. If the newly placed stone is part of a string without
               liberties, remove it and increase the prisoner count.
               In spite of the name "permanent move", this move can
          (usually) be unplayed by `undo_move()', but it is
          significantly more costly than unplaying a temporary move.
          There are limitations on the available move history, so under
          certain circumstances the move may not be possible to unplay
          at a later time.

   * `int undo_move(int n)' 

          Undo `n' permanent moves. Returns 1 if successful and 0 if it
          fails.  If `n' moves cannot be undone, no move is undone.

   Other board functions are documented in *Note Board Utilities::.

\1f
File: gnugo.info,  Node: SGF,  Next: DFA,  Prev: Libboard,  Up: Top

16 Handling SGF trees in memory
*******************************

"SGF" - Smart Game Format - is a file format which is used for storing
game records for a number of different games, among them chess and go.
The format is a framework with special adaptions to each game. This is
not a description of the file format standard. Too see the exact
definition of the file format, see `http://www.red-bean.com/sgf/'.

   GNU Go contains a library to handle go game records in the SGF
format in memory and to read and write SGF files. This library -
`libsgf.a' - is in the `sgf' subdirectory. To use the SGF routines,
include the file `sgftree.h'.

   Each game record is stored as a tree of "nodes", where each node
represents a state of the game, often after some move is made. Each node
contains zero or more "properties", which gives meaning to the node.
There can also be a number of "child nodes" which are different
variations of the game tree. The first child node is the main variation.

   Here is the definition of `SGFNode', and `SGFProperty', the data
structures which are used to encode the game tree.


     typedef struct SGFProperty_t {
       struct SGFProperty_t *next;
       short  name;
       char   value[1];
     } SGFProperty;

     typedef struct SGFNode_t {
       SGFProperty      *props;
       struct SGFNode_t *parent;
       struct SGFNode_t *child;
       struct SGFNode_t *next;
     } SGFNode;

   Each node of the SGF tree is stored in an `SGFNode' struct. It has a
pointer to a linked list of properties (see below) called `props'. It
also has a pointer to a linked list of children, where each child is a
variation which starts at this node. The variations are linked through
the `next' pointer and each variation continues through the `child'
pointer. Each and every node also has a pointer to its parent node (the
`parent' field), except the top node whose parent pointer is `NULL'.

   An SGF property is encoded in the `SGFPoperty' struct. It is linked
in a list through the `next' field.  A property has a `name' which is
encoded in a short int.  Symbolic names of properties can be found in
`sgf_properties.h'.

   Some properties also have a value, which could be an integer, a
floating point value, a character or a string. These values can be
accessed or set through special functions.

16.1 The SGFTree datatype
=========================

Sometimes we just want to record an ongoing game or something similarly
simple and not do any sofisticated tree manipulation.  In that case we
can use the simplified interface provided by `SGFTree' below.


     typedef struct SGFTree_t {
       SGFNode *root;
       SGFNode *lastnode;
     } SGFTree;

   An `SGFTree' contains a pointer to the root node of an SGF tree and
a pointer to the node that we last accessed. Most of the time this will
be the last move of an ongoing game.

   Most of the functions which manipulate an `SGFTree' work exactly
like their `SGFNode' counterparts, except that they work on the current
node of the tree.

   All the functions below that take arguments `tree' and `node' will
work on:

  1. `node' if non-`NULL'

  2. `tree->lastnode' if non-`NULL'

  3. The current end of the game tree.
        in that order.

\1f
File: gnugo.info,  Node: API,  Next: GTP,  Prev: Utility Functions,  Up: Top

17 Application Programmers Interface to GNU Go
**********************************************

If you want to write your own interface to GNU Go, or if you want to
create a go application using the GNU Go engine, this chapter is of
interest to you.

   First an overview: GNU Go consists of two parts: the GNU Go engine
and a program (user interface) which uses this engine. These are linked
together into one binary. The current program implements the following
user modes:

   * An interactive board playable on ASCII terminals

   * solo play - GNU Go plays against itself

   * replay - a mode which lets the user investigate moves in an
     existing SGF file.

   * GMP - Go Modem Protocol, a protocol for automatic play between two
     computers.

   * GTP - Go Text Protocol, a more general go protocol, *note GTP::.
   
   The GNU Go engine can be used in other applications. For example,
supplied with GNU Go is another program using the engine, called
`debugboard', in the directory `interface/debugboard/'. The program
debugboard lets the user load SGF files and can then interactively look
at different properties of the position such as group status and eye
status.

   The purpose of this Chapter is to show how to interface your own
program such as `debugboard' with the GNU Go engine.

   Figure 1 describes the structure of a program using the GNU Go
engine.

                      +-----------------------------------+
                      |                                   |
                      |          Go application           |
                      |                                   |
                      +-----+----------+------+           |
                      |     |          |      |           |
                      |     |   Game   |      |           |
                      |     | handling |      |           |
                      |     |          |      |           |
                      |     +----+-----+      |           |
                      |   SGF    |    Move    |           |
                      | handling | generation |           |
                      |          |            |           |
                      +----------+------------+-----------+
                      |                                   |
                      |           Board handling          |
                      |                                   |
                      +-----------------------------------+

             Figure 1: The structure of a program using the GNU Go engine

   The foundation is a library called `libboard.a' which provides
efficient handling of a go board with rule checks for moves, with
incremental handling of connected strings of stones and with methods to
efficiently hash go positions.

   On top of this, there is a library which helps the application use
Smart Game Format (SGF) files, with complete handling of game trees in
memory and in files. This library is called `libsgf.a'

   The main part of the code within GNU Go is the move generation
library which given a position generates a move. This part of the
engine can also be used to manipulate a go position, add or remove
stones, do tactical and strategic reading and to query the engine for
legal moves. These functions are collected into `libengine.a'.

   The game handling code helps the application programmer keep tracks
of the moves in a game. Games can be saved to SGF files and then later
be read back again. These are also within `libengine.a'.

   The responsibility of the application is to provide the user with a
user interface, graphical or not, and let the user interact with the
engine.

* Menu:

* Getting Started::          How to use the engine in your program
* Basic Data Structures::    Basic Data Structures in the Engine
* The Board State::          The board_state `struct'
* Positional Functions::     Functions which manipulate a Position

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File: gnugo.info,  Node: Getting Started,  Next: Basic Data Structures,  Up: API

17.1 How to use the engine in your own program: getting started
===============================================================

To use the GNU Go engine in your own program you must include the file
`gnugo.h'. This file describes the whole public API. There is another
file, `liberty.h', which describes the internal interface within the
engine. If you want to make a new module within the engine, e.g.  for
suggesting moves you will have to include this file also. In this
section we will only describe the public interface.

   Before you do anything else, you have to call the function
`init_gnugo()'. This function initializes everything within the engine.
It takes one parameter: the number of megabytes the engine can use for
the internal hash table. In addition to this the engine will use a few
megabytes for other purposes such as data describing groups (liberties,
life status, etc), eyes and so on.

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File: gnugo.info,  Node: Basic Data Structures,  Next: The Board State,  Prev: Getting Started,  Up: API

17.2 Basic Data Structures in the Engine
========================================

There are some basic definitions in gnugo.h which are used everywhere.
The most important of these are the numeric declarations of colors.
Each intersection on the board is represented by one of these:


          color              value
          EMPTY                0
          WHITE                1
          BLACK                2

   There is a macro, `OTHER_COLOR(color)' which can be used to get the
other color than the parameter. This macro can only be used on `WHITE'
or `BLACK', but not on `EMPTY'.  

   GNU Go uses two different representations of the board, for most
purposes a one-dimensional one, but for a few purposes a two
dimensional one (*note Libboard::). The one-dimensional board was
introduced before GNU Go 3.2, while the two-dimensional board dates
back to the ancestral program written by Man Lung Li before 1995. The
API still uses the two-dimensional board, so the API functions have not
changed much since GNU Go 3.0.

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File: gnugo.info,  Node: The Board State,  Next: Positional Functions,  Prev: Basic Data Structures,  Up: API

17.3 The board_state struct
===========================

A basic data structure in the engine is the `board_state' struct.  This
structure is internal to the engine and is defined in `liberty.h'.


          typedef unsigned char Intersection;

          struct board_state {
            int board_size;

            Intersection board[BOARDSIZE];
            int board_ko_pos;
            int black_captured;
            int white_captured;

            Intersection initial_board[BOARDSIZE];
            int initial_board_ko_pos;
            int initial_white_captured;
            int initial_black_captured;
            int move_history_color[MAX_MOVE_HISTORY];
            int move_history_pos[MAX_MOVE_HISTORY];
            int move_history_pointer;

            float komi;
            int move_number;
          };

   Here `Intersection' stores `EMPTY', `WHITE' or `BLACK'. It is
currently defined as an `unsigned char' to make it reasonably efficient
in both storage and access time. The board state contains an array of
`Intersection''s representing the board.  The move history is contained
in the struct. Also contained in the struct is the location of a ko
(`EMPTY') if the last move was not a ko capture, the komi, the number
of captures, and corresponding data for the initial position at the
beginning of the move history.

\1f
File: gnugo.info,  Node: Positional Functions,  Prev: The Board State,  Up: API

17.4 Functions which manipulate a Position
==========================================

All the functions in the engine that manipulate Positions have names
prefixed by `gnugo_'. These functions still use the two-dimensional
representation of the board (*note The Board Array::). Here is a
complete list, as prototyped in `gnugo.h':

   * `void init_gnugo(float memory)' 

          Initialize the gnugo engine. This needs to be called once
          only.

   * `void gnugo_clear_board(int boardsize)' 

          Clear the board.

   * `void gnugo_set_komi(float new_komi)' 

          Set the komi.

   * `void gnugo_add_stone(int i, int j, int color)' 

          Place a stone on the board

   * `void gnugo_remove_stone(int i, int j)' 

          Remove a stone from the board

   * `int gnugo_is_pass(int i, int j)' 

          Return true if (i,j) is PASS_MOVE

   * `void gnugo_play_move(int i, int j, int color)' 

          Play a move and start the clock

   * `int gnugo_undo_move(int n)' 

          Undo n permanent moves. Returns 1 if successful and 0 if it
          fails.  If n moves cannot be undone, no move is undone.

   * `int gnugo_play_sgfnode(SGFNode *node, int to_move)' 

          Perform the moves and place the stones from the SGF node on
          the board. Return the color of the player whose turn it is to
          move.

   * `int gnugo_play_sgftree(SGFNode *root, int *until, SGFNode
     **curnode)' 

          Play the moves in ROOT UNTIL movenumber is reached.  Return
          the color of the player whose turn it is to move.

   * `int gnugo_is_legal(int i, int j, int color)' 

          Interface to `is_legal()'.

   * `int gnugo_is_suicide(int i, int j, int color)' 

          Interface to `is_suicide()'.

   * `int gnugo_placehand(int handicap)' 

          Interface to placehand. Sets up handicap pieces and returns
          the number of placed handicap stones.

   * `void gnugo_recordboard(SGFNode *root)' 

          Interface to `sgffile_recordboard()'

   * `int gnugo_sethand(int handicap, SGFNode *node)' 

          Interface to placehand. Sets up handicap stones and returns
          the number of placed handicap stones, updating the sgf file

   * `float gnugo_genmove(int *i, int *j, int color, int *resign)' 

          Interface to `genmove()'.

   * `int gnugo_attack(int m, int n, int *i, int *j)' 

          Interface to `attack()'.

   * `int gnugo_find_defense(int m, int n, int *i, int *j)' 

          Interface to `find_defense()'.

   * `void gnugo_who_wins(int color, FILE *outfile)' 

          Interface to `who_wins()'.

   * `float gnugo_estimate_score(float *upper, float *lower)' 

          Put upper and lower score estimates into `*upper', `*lower'
          and return the average. A positive score favors white. In
          computing the upper bound, `CRITICAL' dragons are awarded to
          white; in computing the lower bound, they are awarded to
          black.

   * `void gnugo_examine_position(int color, int how_much)' 

          Interface to `examine_position'.

   * `int gnugo_get_komi()' 

          Report the komi.

   * `void gnugo_get_board(int b[MAX_BOARD][MAX_BOARD])' 

          Place the board into the `b' array.

   * `int gnugo_get_boardsize()' 

          Report the board size.

   * `int gnugo_get_move_number()' 

          Report the move number.

17.5 Game handling
==================

The functions (in *note Positional Functions::) are all that are needed
to create a fully functional go program.  But to make the life easier
for the programmer, there is a small set of functions specially
designed for handling ongoing games.

   The data structure describing an ongoing game is the `Gameinfo'. It
is defined as follows:


     typedef struct {
       int       handicap;

       int       to_move;            /* whose move it currently is */
       SGFTree   game_record;        /* Game record in sgf format. */

       int       computer_player;    /* BLACK, WHITE, or EMPTY (used as BOTH) */

       char      outfilename[128];   /* Trickle file */
       FILE      *outfile;
     } Gameinfo;

   The meaning of `handicap' should be obvious. `to_move' is the color
of the side whose turn it is to move.

   The SGF tree `game_record' is used to store all the moves in the
entire game, including a header node which contains, among other
things, komi and handicap.

   If one or both of the opponents is the computer, the field
`computer_player' is used. Otherwise it can be ignored.

   GNU Go can use a trickle file to continuously save all the moves of
an ongoing game. This file can also contain information about internal
state of the engine such as move reasons for various locations or move
valuations. The name of this file should be stored in `outfilename' and
the file pointer to the open file is stored in `outfile'. If no trickle
file is used, `outfilename[0]' will contain a null character and
`outfile' will be set to `NULL'.

17.5.1 Functions which manipulate a Gameinfo
--------------------------------------------

All the functions in the engine that manipulate Gameinfos have names
prefixed by `gameinfo_'.  Here is a complete list, as prototyped in
`gnugo.h':

   * `void gameinfo_clear(Gameinfo *ginfo, int boardsize, float komi)' 

          Initialize the `Gameinfo' structure.

   * `void gameinfo_print(Gameinfo *ginfo)' 

          Print a gameinfo.

   * `void gameinfo_load_sgfheader(Gameinfo *gameinfo, SGFNode *head)' 

          Reads header info from sgf structure and sets the appropriate
          variables.

   * `void gameinfo_play_move(Gameinfo *ginfo, int i, int j, int color)' 

          Make a move in the game. Return 1 if the move was legal. In
          that case the move is actually done. Otherwise return 0.

   * `int gameinfo_play_sgftree_rot(Gameinfo *gameinfo, SGFNode *head,
     const char *untilstr, int orientation)' 

          Play the moves in an SGF tree. Walk the main variation,
          actioning the properties into the playing board. Returns the
          color of the next move to be made. Head is an sgf tree.
          Untilstr is an optional string of the form either 'L12' or
          '120' which tells it to stop playing at that move or move
          number. When debugging, this is the location of the move
          being examined.

   * `int gameinfo_play_sgftree(Gameinfo *gameinfo, SGFNode *head,
     const char *untilstr)' 

          Same as previous function, using standard orientation.

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File: gnugo.info,  Node: Utility Functions,  Next: API,  Prev: DFA,  Up: Top

18 Utility Functions
********************

In this Chapter, we document some of the utilities which may be called
from the GNU Go engine.

* Menu:

* General Utilities::              Utilities from `engine/utils.c'
* Print Utilities::                Utilities from `engine/printutils.c'
* Board Utilities::                Utilities from `engine/board.c'
* Influence Utilities::		   Utilities from `engine/influence.c'

\1f
File: gnugo.info,  Node: General Utilities,  Next: Print Utilities,  Up: Utility Functions

18.1 General Utilities
======================

Utility functions from `engine/utils.c'. Many of these functions
underlie autohelper functions (*note Autohelper Functions::).

   * `void change_dragon_status(int dr, int status)' 

          Change the status of all the stones in the dragon at `dr'.

   * `int defend_against(int move, int color, int apos)' 

          Check whether a move at `move' stops the enemy from playing
          at (apos).

   * `int cut_possible(int pos, int color)'

          Returns true if `color' can cut at `pos', or if connection
          through `pos' is inhibited. This information is collected by
          `find_cuts()', using the B patterns in the connections
          database.

   * `int does_attack(int move, int str)' 

          returns true if the move at `move' attacks `str'. This means
          that it captures the string, and that `str' is not already
          dead.

   * `int does_defend(int move, int str)' 

          `does_defend(move, str)' returns true if the move at `move'
          defends `str'. This means that it defends the string, and that
          `str' can be captured if no defense is made.

   * `int somewhere(int color, int last_move, ...)' 

          Example: `somewhere(WHITE, 2, apos, bpos, cpos)'.  Returns
          true if one of the vertices listed satisfies
          `board[pos]==color'. Here num_moves is the number of moves
          minus one.  If the check is true the dragon is not allowed to
          be dead. This check is only valid if `stackp==0'.

   * `int visible_along_edge(int color, int apos, int bpos)'

          Search along the edge for the first visible stone. Start at
          apos and move in the direction of bpos. Return 1 if the first
          visible stone is of the given color. It is required that apos
          and bpos are at the same distance from the edge.

   * `int test_symmetry_after_move(int move, int color, int strict)' 

          Is the board symmetric (or rather antisymmetric) with respect
          to mirroring in tengen after a specific move has been played?
          If the move is PASS_MOVE, check the current board.  If strict
          is set we require that each stone is matched by a stone of
          the opposite color at the mirrored vertex. Otherwise we only
          require that each stone is matched by a stone of either color.

   * `int play_break_through_n(int color, int num_moves, ...)' 

          The function `play_break_through_n()' plays a sequence of
          moves, alternating between the players and starting with
          color. After having played through the sequence, the three
          last coordinate pairs gives a position to be analyzed by
          `break_through()', to see whether either color has managed to
          enclose some stones and/or connected his own stones. If any
          of the three last positions is empty, it's assumed that the
          enclosure has failed, as well as the attempt to connect. If
          one or more of the moves to play turns out to be illegal for
          some reason, the rest of the sequence is played anyway, and
          `break_through()' is called as if nothing special happened.
          Like `break_through()', this function returns 1 if the
          attempt to break through was succesful and 2 if it only
          managed to cut through.

   * `int play_attack_defend_n(int color, int do_attack, int num_moves,
     ...)'

   * `int play_attack_defend2_n(int color, int do_attack, int
     num_moves, ...)' 

          The function `play_attack_defend_n()' plays a sequence of
          moves, alternating between the players and starting with
          `color'. After having played through the sequence, the last
          coordinate pair gives a target to attack or defend, depending
          on the value of do_attack.  If there is no stone present to
          attack or defend, it is assumed that it has already been
          captured. If one or more of the moves to play turns out to be
          illegal for some reason, the rest of the sequence is played
          anyway, and attack/defense is tested as if nothing special
          happened. Conversely, `play_attack_defend2_n()' plays a
          sequence of moves, alternating between the players and
          starting with `color'. After having played through the
          sequence, the two last coordinate pairs give two targets to
          simultaneously attack or defend, depending on the value of
          do_attack. If there is no stone present to attack or defend,
          it is assumed that it has already been captured. If one or
          more of the moves to play turns out to be illegal for some
          reason, the rest of the sequence is played anyway, and
          attack/defense is tested as if nothing special happened.  A
          typical use of these functions is to set up a ladder in an
          autohelper and see whether it works or not.

   * `int play_connect_n(int color, int do_connect, int num_moves, ...)' 

          Plays a sequence of moves, alternating between the players
          and starting with `color'. After having played through the
          sequence, the two last coordinates give two targets that
          should be connected or disconnected, depending on the value
          of do_connect. If there is no stone present to connect or
          disconnect, it is assumed that the connection has failed. If
          one or more of the moves to play turns out to be illegal for
          some reason, the rest of the sequence is played anyway, and
          connection/disconnection is tested as if nothing special
          happened.  Ultimately the connection is decided by the
          functions `string_connect' and `disconnect' (*note Connection
          Reading::).

   * `void set_depth_values(int level)' 

          It is assumed in reading a ladder if `stackp >= depth' that
          as soon as a bounding stone is in atari, the string is safe.
          Similar uses are made of the other depth parameters such as
          `backfill_depth' and so forth. In short, simplifying
          assumptions are made when `stackp' is large. Unfortunately
          any such scheme invites the "horizon effect," in which a
          stalling move is perceived as a win, by pushing the
          refutation past the "horizon"--the value of `stackp' in which
          the reading assumptions are relaxed. To avoid the depth it is
          sometimes necessary to increase the depth parameters. This
          function can be used to set the various reading depth
          parameters. If `mandated_depth_value' is not -1 that value is
          used; otherwise the depth values are set as a function of
          level. The parameter `mandated_depth_value' can be set at the
          command line to force a particular value of depth; normally
          it is -1.

   * `void modify_depth_values(int n)' 

          Modify the various tactical reading depth parameters. This is
          typically used to avoid horizon effects. By temporarily
          increasing the depth values when trying some move, one can
          avoid that an irrelevant move seems effective just because
          the reading hits a depth limit earlier than it did when
          reading only on relevant moves.

   * `void increase_depth_values(void)' 

          `modify_depth_values(1)'.

   * `void decrease_depth_values(void)' 

          `modify_depth_values(-1)'.

   * `void restore_depth_values()' 

          Sets `depth' and so forth to their saved values.

   * `void set_temporary_depth_values(int d, int b, int b2, int bc, int
     ss, int br, int f, int k)'

          Explicitly set the depth values. This function is currently
          never called.

   * `int confirm_safety(int move, int color, int *defense_point, char
     safe_stones[BOARDMAX])' 

          Check that the move at color doesn't involve any kind of
          blunder, regardless of size.

   * `float blunder_size(int move, int color, int *defense_point, char
     safe_stones[BOARDMAX])' 

          This function will detect some blunders. If the move reduces
          the number of liberties of an adjacent friendly string, there
          is a danger that the move could backfire, so the function
          checks that no friendly worm which was formerly not
          attackable becomes attackable, and it checks that no opposing
          worm which was not defendable becomes defendable.  It returns
          the estimated size of the blunder, or 0.0 if nothing bad has
          happened.  The array `safe_stones[]' contains the stones that
          are supposedly safe after `move'. It may be `NULL'. For use
          when called from `fill_liberty()', this function may
          optionally return a point of defense, which, if taken, will
          presumably make the move at `move' safe on a subsequent turn.

   * `int double_atari(int move, int color, float *value, char
     safe_stones[BOARDMAX])' 

          Returns true if a move by (color) fits the following shape:
                   X*        (O=color)
                   OX
          capturing one of the two `X' strings. The name is a slight
          misnomer since this includes attacks which are not
          necessarily double ataris, though the common double atari is
          the most important special case. If `safe_stones != NULL',
          then only attacks on stones marked as safe are tried. The
          value of the double atari attack is returned in value (unless
          value is `NULL'), and the attacked stones are marked unsafe.

   * `void unconditional_life(int unconditional_territory[BOARDMAX],
     int color)' 

          Find those worms of the given color that can never be
          captured, even if the opponent is allowed an arbitrary number
          of consecutive moves. The coordinates of the origins of these
          worms are written to the worm arrays and the number of
          non-capturable worms is returned.  The algorithm is to cycle
          through the worms until none remains or no more can be
          captured. A worm is removed when it is found to be
          capturable, by letting the opponent try to play on all its
          liberties. If the attack fails, the moves are undone. When no
          more worm can be removed in this way, the remaining ones are
          unconditionally alive.  After this, unconditionally dead
          opponent worms and unconditional territory are identified. To
          find these, we continue from the position obtained at the end
          of the previous operation (only unconditionally alive strings
          remain for color) with the following steps:

            1. Play opponent stones on all liberties of the
               unconditionally alive strings except where illegal.
               (That the move order may determine exactly which
               liberties can be played legally is not important. Just
               pick an arbitrary order).

            2. Recursively extend opponent strings in atari, except
               where this would be suicide.

            3. Play an opponent stone anywhere it can get two empty
               neighbors. (I.e. split big eyes into small ones).

            4. an opponent stone anywhere it can get one empty
               neighbor. (I.e. reduce two space eyes to one space eyes.)
               Remaining opponent strings in atari and remaining
               liberties of the unconditionally alive strings
               constitute the unconditional territory.  Opponent
               strings from the initial position placed on
               unconditional territory are unconditionally dead.  On
               return, `unconditional_territory[][]' is 1 where color
               has unconditionally alive stones, 2 where it has
               unconditional territory, and 0 otherwise.

   * `void who_wins(int color, FILE *outfile)'

          Score the game and determine the winner

   * `void find_superstring(int str, int *num_stones, int *stones)' 

          Find the stones of an extended string, where the extensions
          are through the following kinds of connections:
            1. Solid connections (just like ordinary string).
                        OO

            2. Diagonal connection or one space jump through an
               intersection where an opponent move would be suicide or
               self-atari.
                        ...
                        O.O
                        XOX
                        X.X

            3. Bamboo joint.
                        OO
                        ..
                        OO

            4. Diagonal connection where both adjacent intersections
               are empty.
                        .O
                        O.

            5. Connection through adjacent or diagonal tactically
               captured stones.  Connections of this type are omitted
               when the superstring code is called from reading.c, but
               included when the superstring code is called from owl.c

   * `void find_superstring_liberties(int str, int *num_libs, int
     *libs, int liberty_cap)' 

          This function computes the superstring at `str' as described
          above, but omitting connections of type 5. Then it constructs
          a list of liberties of the superstring which are not already
          liberties of `str'.  If `liberty_cap' is nonzero, only
          liberties of substrings of the superstring which have fewer
          than `liberty_cap' liberties are generated.

   * `void find_proper_superstring_liberties(int str, int *num_libs,
     int *libs, int liberty_cap)' 

          This function is the same as find_superstring_liberties, but
          it omits those liberties of the string `str', presumably
          since those have already been treated elsewhere.  If
          `liberty_cap' is nonzero, only liberties of substrings of the
          superstring which have at most `liberty_cap' liberties are
          generated.

   * `void find_superstring_stones_and_liberties(int str, int
     *num_stones, int *stones, int *num_libs, int *libs, int
     liberty_cap)' 

          This function computes the superstring at `str' as described
          above, but omitting connections of type 5. Then it constructs
          a list of liberties of the superstring which are not already
          liberties of `str'. If liberty_cap is nonzero, only liberties
          of substrings of the superstring which have fewer than
          liberty_cap liberties are generated.

   * `void superstring_chainlinks(int str, int *num_adj, int
     adjs[MAXCHAIN], int liberty_cap)' 

          analogous to chainlinks, this function finds boundary chains
          of the superstring at `str', including those which are
          boundary chains of `str' itself. If `liberty_cap != 0', only
          those boundary chains with `<= liberty_cap' liberties are
          reported.

   * `void proper_superstring_chainlinks(int str, int *num_adj, int
     adjs[MAXCHAIN], int liberty_cap)' 

          analogous to chainlinks, this function finds boundary chains
          of the superstring at `str', omitting those which are
          boundary chains of `str' itself. If `liberty_cap != 0', only
          those boundary chains with `<= liberty_cap' liberties are
          reported.

   * `void start_timer(int n)' 

          Start a timer. GNU Go has four internal timers available for
          assessing the time spent on various tasks.

   * `double time_report(int n, const char *occupation, int move,
     double mintime)' 

          Report time spent and restart the timer. Make no report if
          elapsed time is less than mintime.

\1f
File: gnugo.info,  Node: Print Utilities,  Next: Board Utilities,  Prev: General Utilities,  Up: Utility Functions

18.2 Print Utilities
====================

Functions in `engine/printutils.c' do formatted printing similar to
`printf' and its allies.  The following formats are recognized:

   * `%c', `%d', `%f', `%s', `%x'

          These have their usual meaning in formatted output, printing
          a character, integer, float, string or hexadecimal,
          respectively.

   * `%o'

          `Outdent.' Normally output is indented by `2*stackp' spaces,
          so that the depth can be seen at a glance in traces. At the
          beginning of a format, this `%o' inhibits the indentation.

   * `%H'

          Print a hashvalue.

   * `%C'

          Print a color as a string.

   * `%m', `%2m' (synonyms)

          Takes 2 integers and writes a move, using the two dimensional
          board representation (*note The Board Array::)

   * `%1m'

          Takes 1 integers and writes a move, using the one dimensional
          board representation (*note The Board Array::)

   We list the non statically declared functions in `printutils.c'.

   * `void gfprintf(FILE *outfile, const char *fmt, ...)' 

          Formatted output to `outfile'.

   * `int gprintf(const char *fmt, ...)' 

          Formatted output to stderr. Always returns 1 to allow use in
          short-circuit logical expressions.

   * `int mprintf(const char *fmt, ...)' 

          Formatted output to stdout.

   * `DEBUG(level, fmt, args...)' 

          If `level & debug', do formatted output to stderr. Otherwise,
          ignore.

   * `void abortgo(const char *file, int line, const char *msg, int
     pos)' 

          Print debugging output in an error situation, then exit.

   * `const char * color_to_string(int color)' 

          Convert a color value to a string

   * `const char * location_to_string(int pos)' 

          Convert a location to a string

   * `void location_to_buffer(int pos, char *buf)' 

          Convert a location to a string, writing to a buffer.

   * `int string_to_location(int boardsize, char *str, int *m, int *n)' 

          Get the `(m, n)' coordinates in the standard GNU Go
          coordinate system from the string `str'.  This means that `m'
          is the nth row from the top and `n' is the column. Both
          coordinates are between 0 and `boardsize-1', inclusive.
          Return 1 if ok, otherwise return 0;

   * `int is_hoshi_point(int m, int n)' True if the coordinate is a
     hoshi point.

   * `void draw_letter_coordinates(FILE *outfile)' Print a line with
     coordinate letters above the board.

   * `void simple_showboard(FILE *outfile)' 

          Bare bones version of `showboard(0)'. No fancy options, no
          hint of color, and you can choose where to write it.

   The following functions are in `showbord.c'. Not all public
functions in that file are listed here.

   * `void showboard(int xo)' 

          Show go board.
               xo=0:      black and white XO board for ascii game
               xo=1:      colored dragon display
               xo=2:      colored eye display
               xo=3:      colored owl display
               xo=4:      colored matcher status display

   * `const char * status_to_string(int status)' 

          Convert a status value to a string.

   * `const char * safety_to_string(int status)' 

          Convert a safety value to a string.

   * `const char * result_to_string(int result)' 

          Convert a read result to a string

\1f
File: gnugo.info,  Node: Board Utilities,  Next: Influence Utilities,  Prev: Print Utilities,  Up: Utility Functions

18.3 Board Utilities
====================

The functions documented in this section are from `board.c'. Other
functions in `board.c' are described in *Note Some Board Functions::.

   * `void store_board(struct board_state *state)' 

          Save board state.

   * `void restore_board(struct board_state *state)' 

          Restore a saved board state.

   * `void clear_board(void)' 

          Clear the internal board.

   * `void dump_stack(void)' 

          for use under GDB prints the move stack.

   * `void add_stone(int pos, int color)' 

          Place a stone on the board and update the board_hash. This
          operation destroys all move history.

   * `void remove_stone(int pos)' 

          Remove a stone from the board and update the board_hash. This
          operation destroys the move history.

   * `int is_pass(int pos)' 

          Test if the move is a pass or not.  Return 1 if it is.

   * `int  is_legal(int pos, int color)' 

          Determines whether the move `color' at `pos' is legal.

   * `int  is_suicide(int pos, int color)' 

          Determines whether the move `color' at `pos' would be a
          suicide.  This is the case if
            1. There is no neighboring empty intersection.

            2. There is no neighboring opponent string with exactly one
               liberty.

            3. There is no neighboring friendly string with more than
               one liberty.

   * `int is_illegal_ko_capture(int pos, int color)' 

          Determines whether the move `color' at `pos' would be an
          illegal ko capture.

   * `int is_edge_vertex(int pos)' 

          Determine whether vertex is on the edge.

   * `int edge_distance(int pos)' 

          Distance to the edge.

   * `int is_corner_vertex(int pos)' 

          Determine whether vertex is a corner.

   * `int get_komaster()' 

   * `int get_kom_pos()' 

          Public functions to access the variable `komaster' and
          `kom_pos', which are static in `board.c'.

   Next we come to `countlib()' and its allies, which address the
problem of determining how many liberties a string has. Although
`countlib()' addresses this basic question, other functions can often
get the needed information more quickly, so there are a number of
different functions in this family.

   * `int countlib(int str)' 

          Count the number of liberties of the string at `pos'. There
          must be a stone at this location.

   * `int findlib(int str, int maxlib, int *libs)' 

          Find the liberties of the string at `str'. This location must
          not be empty. The locations of up to maxlib liberties are
          written into `libs[]'. The full number of liberties is
          returned.  If you want the locations of all liberties,
          whatever their number, you should pass `MAXLIBS' as the value
          for `maxlib' and allocate space for `libs[]' accordingly.

   * `int fastlib(int pos, int color, int ignore_captures)' 

          Count the liberties a stone of the given color would get if
          played at `pos'. The intent of this function is to be as fast
          as possible, not necessarily complete. But if it returns a
          positive value (meaning it has succeeded), the value is
          guaranteed to be correct. Captures are ignored based if the
          `ignore_captures' field is nonzero. The location `pos' must
          be empty.  The function fails if there are more than two
          neighbor strings of the same color.  In this case, the return
          value is -1.  Captures are handled in a very limited way, so
          if ignore_capture is 0, and a capture is required, it will
          often return -1.

   * `int approxlib(int pos, int color, int maxlib, int *libs)' 

          Find the liberties a stone of the given color would get if
          played at `pos', ignoring possible captures of opponent
          stones.  The location `pos' must be empty. If `libs != NULL',
          the locations of up to `maxlib' liberties are written into
          `libs[]'. The counting of liberties may or may not be halted
          when `maxlib' is reached. The number of liberties found is
          returned, which may be less than the total number of
          liberties if `maxlib' is small. If you want the number or the
          locations of all liberties, however many they are, you should
          pass `MAXLIBS' as the value for maxlib and allocate space for
          `libs[]' accordingly.

   * `int accuratelib(int pos, int color, int maxlib, int *libs)' 

          Find the liberties a stone of the given color would get if
          played at `pos'. This function takes into consideration all
          captures. Its return value is exact in that sense it counts
          all the liberties, unless `maxlib' allows it to stop earlier.
          The location `pos' must be empty. If `libs != NULL', the
          locations of up to `maxlib' liberties are written into
          `libs[]'. The counting of liberties may or may not be halted
          when `maxlib' is reached. The number of found liberties is
          returned.  This function guarantees that liberties which are
          not results of captures come first in `libs[]' array. To find
          whether all the liberties starting from a given one are
          results of captures, one may use `if (board[libs[k]] !=
          EMPTY)' construction.  If you want the number or the
          locations of all liberties, however many they are, you should
          pass `MAXLIBS' as the value for `maxlib' and allocate space
          for `libs[]' accordingly.

   Next we have some general utility functions.

   * `int count_common_libs(int str1, int str2)' 

          Find the number of common liberties of the two strings.

   * `int find_common_libs(int str1, int str2, int maxlib, int *libs)' 

          Find the common liberties of the two strings. The locations
          of up to `maxlib' common liberties are written into `libs[]'.
          The full number of common liberties is returned.  If you want
          the locations of all common liberties, whatever their number,
          you should pass `MAXLIBS' as the value for `maxlib' and
          allocate space for `libs[]' accordingly.

   * `int have_common_lib(int str1, int str2, int *lib)' 

          Determine whether two strings have at least one common
          liberty.  If they do and `lib != NULL', one common liberty is
          returned in `*lib'.

   * `int countstones(int str)' 

          Report the number of stones in a string.

   * `int findstones(int str, int maxstones, int *stones)' 

          Find the stones of the string at `str'. The location must not
          be empty. The locations of up to maxstones stones are written
          into `stones[]'. The full number of stones is returned.

   * `int  chainlinks(int str, int adj[MAXCHAIN])' 

          This very useful function returns (in the `adj' array) the
          chains surrounding the string at `str'. The number of chains
          is returned.

   * `int chainlinks2(int str, int adj[MAXCHAIN], int lib)' 

          Returns (in `adj' array) those chains surrounding the string
          at `str', which has exactly `lib' liberties. The number of
          such chains is returned.

   * `int chainlinks3(int str, int adj[MAXCHAIN], int lib)' 

          Returns (in `adj' array) the chains surrounding the string at
          `str', which have less or equal `lib' liberties.  The number
          of such chains is returned.

   * `int extended_chainlinks(int str, int adj[MAXCHAIN], int
     both_colors)' 

          Returns (in the `adj' array) the opponent strings being
          directly adjacent to `str' or having a common liberty with
          `str'. The number of such strings is returned.  If the
          both_colors parameter is true, also own strings sharing a
          liberty are returned.

   * `int find_origin(int str)' 

          Find the origin of a string, i.e. the point with the smallest
          1D board coordinate. The idea is to have a canonical
          reference point for a string.

   * `int is_self_atari(int pos, int color)' 

          Determine whether a move by color at `pos' would be a self
          atari, i.e. whether it would get more than one liberty. This
          function returns true also for the case of a suicide move.

   * `int liberty_of_string(int pos, int str)' 

          Returns true if `pos' is a liberty of the string at `str'.

   * `int second_order_liberty_of_string(int pos, int str)' 

          Returns true if `pos' is a second order liberty of the string
          at str.

   * `int neighbor_of_string(int pos, int str)' 

          Returns true if `pos' is adjacent to the string at `str'.

   * `int has_neighbor(int pos, int color)' 

          Returns true if `pos' has a neighbor of `color'.

   * `int same_string(int str1, int str2)' 

          Returns true if `str1' and `str2' belong to the same string.

   * `int adjacent_strings(int str1, int str2)' 

          Returns true if the strings at `str1' and `str2' are adjacent.

   * `int is_ko(int pos, int color, int *ko_pos)' 

          Return true if the move `pos' by `color' is a ko capture
          (whether capture is legal on this move or not). If so, and if
          `ko_pos' is not a `NULL' pointer, then `*ko_pos' returns the
          location of the captured ko stone.  If the move is not a ko
          capture, `*ko_pos' is set to 0.  A move is a ko capture if
          and only if
            1. All neighbors are opponent stones.

            2. The number of captured stones is exactly one.

   * `int is_ko_point(int pos)' 

          Return true if `pos' is either a stone, which if captured
          would give ko, or if `pos' is an empty intersection adjacent
          to a ko stone.

   * `int does_capture_something(int pos, int color)' 

          Returns 1 if at least one string is captured when color plays
          at `pos'.

   * `void mark_string(int str, char mx[BOARDMAX], char mark)' 

          For each stone in the string at pos, set `mx' to value mark.
          If some of the stones in the string are marked prior to
          calling this function, only the connected unmarked stones
          starting from pos are guaranteed to become marked. The rest
          of the string may or may not become marked. (In the current
          implementation, it will.)

   * `int move_in_stack(int pos, int cutoff)' 

          Returns true if at least one move has been played at pos at
          deeper than level `cutoff' in the reading tree.

   * `int stones_on_board(int color)' 

          Return the number of stones of the indicated color(s) on the
          board.  This only counts stones in the permanent position,
          not stones placed by `trymove()' or `tryko()'. Use
          `stones_on_board(BLACK | WHITE)' to get the total number of
          stones on the board.

\1f
File: gnugo.info,  Node: Influence Utilities,  Prev: Board Utilities,  Up: Utility Functions

18.4 Utilities from `engine/influence.c'
========================================

We will only list here a portion of the public functions in
`influence.c'.  The influence code is invoked through the function
`compute_influence' (*note Influence Usage::). It is invoked as follows.

   * `void compute_influence(int color, const char
     safe_stones[BOARDMAX], const float strength[BOARDMAX], struct
     influence_data *q, int move, const char *trace_message)' 

          Compute the influence values for both colors.  The caller must
             - set up the `board[]' state

             - mark safe stones with `INFLUENCE_SAFE_STONE', dead
               stones with 0

             - mark stones newly saved by a move with
               `INFLUENCE_SAVED_STONE' (this is relevant if the
               influence_data *q is reused to compute a followup value
               for this move).
          Results will be stored in q.  `move' has no effects except
          toggling debugging. Set it to -1 for no debug output at all
          (otherwise it will be controlled by the `-m' command line
          option). It is assumed that `color' is in turn to move. (This
          affects the barrier patterns (class A, D) and intrusions
          (class B)). Color

   Other functions in `influence.c' are of the nature of utilities
which may be useful throughout the engine. We list the most useful ones
here.

   * `void influence_mark_non_territory(int pos, int color)' 

          Called from actions for `t' patterns in `barriers.db'.  Marks
          `pos' as not being territory for `color'.

   * `int whose_territory(const struct influence_data *q, int pos)' 

          Return the color of the territory at `pos'. If it's territory
          for neither color, `EMPTY' is returned.

   * `int whose_moyo(const struct influence_data *q, int pos)' 

          Return the color who has a moyo at `pos'. If neither color
          has a moyo there, `EMPTY' is returned. The definition of moyo
          in terms of the influences is totally ad hoc.

   * `int whose_area(const struct influence_data *q, int pos)' 

          Return the color who has dominating influence ("area") at
          `pos'.  If neither color dominates the influence there, EMPTY
          is returned.  The definition of area in terms of the
          influences is totally ad hoc.

\1f
File: gnugo.info,  Node: GTP,  Next: Regression,  Prev: API,  Up: Top

19 The Go Text Protocol
***********************

* Menu:

* The Go Text Protocol::          The Go Text Protocol
* Running in GTP mode::           Running GNU Go in GTP mode
* GTP applications::              GTP applications
* The Metamachine::               The Metamachine
* Adding new GTP commands::       Adding new GTP commands
* GTP command reference::         Details on every GTP command

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File: gnugo.info,  Node: The Go Text Protocol,  Next: Running in GTP mode,  Up: GTP

19.1 The Go Text Protocol
=========================

GNU Go 3.0 introduced a new interface, the Go Text Protocol, abbreviated
GTP. The intention was to make an interface that is better suited for
machine-machine communication than the ascii interface and simpler, more
powerful, and more flexible than the Go Modem Protocol.

   There are two versions of the protocol. Version 1 was used with GNU
Go 3.0 and 3.2. GNU Go 3.4 and later versions use protocol version 2.
The specification of GTP version 2 is available at
`http://www.lysator.liu.se/~gunnar/gtp/'. GNU Go 3.4 is the reference
implementation for GTP version 2, but all but the most common commands
are to be regarded as private extensions of the protocol.

   The GTP has a variety of applications. For GNU Go the first use was
in regression testing (*note Regression::), followed by communication
with the NNGS go server and for automated test games against itself and
other programs. Now there are also many graphical user interfaces
available supporting GTP, as well as bridges to other Go servers than
NNGS.

\1f
File: gnugo.info,  Node: Running in GTP mode,  Next: GTP applications,  Prev: The Go Text Protocol,  Up: GTP

19.2 Running GNU Go in GTP mode
===============================

To start GNU Go in GTP mode, simply invoke it with the option `--mode
gtp'. You will not get a prompt or any other output to start with but
GNU Go is silently waiting for GTP commands.

   A sample GTP session may look as follows:

     virihaure 462% ./gnugo --mode gtp
     1 boardsize 7
     =1

     2 clear_board
     =2

     3 play black D5
     =3

     4 genmove white
     =4 C3

     5 play black C3
     ?5 illegal move

     6 play black E3
     =6

     7 showboard
     =7
        A B C D E F G
      7 . . . . . . . 7
      6 . . . . . . . 6
      5 . . + X + . . 5
      4 . . . + . . . 4
      3 . . O . X . . 3
      2 . . . . . . . 2     WHITE (O) has captured 0 stones
      1 . . . . . . . 1     BLACK (X) has captured 0 stones
        A B C D E F G

     8 quit
     =8

   Commands are given on a single line, starting by an optional identity
number, followed by the command name and its arguments.

   If the command is successful, the response starts by an equals sign
(`='), followed by the identity number of the command (if any) and then
the result. In this example all results were empty strings except for
command 4 where the answer was the white move at C3, and command 7
where the result was a diagram of the current board position. The
response ends by two consecutive newlines.

   Failing commands are signified by a question mark (`?') instead of
an equals sign, as in the response to command 5.

   The detailed specification of the protocol can be found at
`http://www.lysator.liu.se/~gunnar/gtp/'. The available commands in GNU
Go may always be listed using the command `list_commands'.  They are
also documented in *Note GTP command reference::.

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File: gnugo.info,  Node: GTP applications,  Next: The Metamachine,  Prev: Running in GTP mode,  Up: GTP

19.3 GTP applications
=====================

GTP is an asymmetric protocol involving two parties which we call
controller and engine. The controller sends all commands and the engine
only responds to these commands. GNU Go implements the engine end of the
protocol.

   With the source code of GNU Go is also distributed a number of
applications implementing the controller end. Among the most
interesting of these are:

   * `regression/regress.awk'

          Script to run regressions. The script sends GTP commands to
          set up and evaluate positions to the engine and then analyzes
          the responses from the engine. More information about GTP
          based regression testing can be found in the regression
          chapter (*note Regression::).

   * `regression/regress.pl'

          Perl script to run regressions, giving output which together
          with the CGI script `regression/regress.plx' generates HTML
          views of the regressions.

   * `regression/regress.pike'

          Pike script to run regressions. More feature-rich and
          powerful than `regress.awk'.

   * `regression/view.pike'

          Pike script to examine a single regression testcase through a
          graphical board. This gives an easy way to inspect many of
          the GNU Go internals.

   * `interface/gtp_examples/twogtp'

          Perl script to play two engines against each other. The script
          essentially sets up both engines with desired boardsize,
          handicap, and komi, then relays moves back and forth between
          the engines.

   * `interface/gtp_examples/twogtp-a'

          An alternative Perl implementation of twogtp.

   * `interface/gtp_examples/twogtp.py'

          Implementation of twogtp in Python. Has more features than
          the Perl variants.

   * `interface/gtp_examples/twogtp.pike'

          Implementation of twogtp in Pike. Has even more features than
          the Python variant.

   * `interface/gtp_examples/2ptkgo.pl'

          Variation of twogtp which includes a graphical board.

   More GTP applications, including bridges to go servers and graphical
user interfaces, are listed at `http://www.lysator.liu.se/~gunnar/gtp/'.

\1f
File: gnugo.info,  Node: The Metamachine,  Next: Adding new GTP commands,  Prev: GTP applications,  Up: GTP

19.4 The Metamachine
====================

An interesting application of the GTP is the concept of using GNU Go as
an "Oracle" that can be consulted by another process. This could be
another computer program that asks GNU Go to generate future board
positions, then evaluate them.

   David Doshay at the University of California at Santa Cruz has done
interesting experiments with a parallel engine, known as SlugGo, that
is based on GNU Go.  These are described in
`http://lists.gnu.org/archive/html/gnugo-devel/2004-08/msg00060.html'.

   The "Metamachine" experiment is a more modest approach using the GTP
to communicate with a GNU Go process that is used as an oracle. The
following scheme is used.

   * The GNU Go "oracle" is asked to generate its top moves using the
     GTP `top_moves' commands.

   * Both moves are tried and `estimate_score' is called from the
     resulting board position.

   * The higher scoring position is selected as the engine's move.

   This scheme does not produce a stronger engine, but it is
suggestive, and the SlugGo experiment seems to show that a more
elaborate scheme along the same lines could produce a stronger engine.

   Two implementations are distributed with GNU Go. Both make use of
`fork' and `pipe' system calls, so they require a Unix-like
environment.  The Metamachine has been tested under GNU/Linux.

   *Important:* If the Metamachine terminates normally, the GNU Go
process will be killed. However there is a danger that something will
go wrong. When you are finished running the Metamachine, it is a good
idea to run `ps -A|grep gnugo' or `ps -aux|grep gnugo' to make sure
there are no unterminated processes. (If there are, just kill them.)

19.4.1 The Standalone Metamachine
---------------------------------

In `interface/gtp_examples/metamachine.c' is a standalone
implementation of the Metamachine. Compile it with `cc -o metamachine
metamachine.c' and run it. It forks a `gnugo' process with which it
communicates through the GTP, to use as an oracle.

   The following scheme is followed:

                  stdin             pipe a
       GTP client ----> Metamachine -----> GNU Go
                  <----             <-----
                 stdout             pipe b

   Most commands issued by the client are passed along verbatim to GNU
Go by the Metamachine. The exception is gg_genmove, which is
intercepted then processed differently, as described above. The client
is unaware of this, and only knows that it issued a gg_genmove command
and received a reply.  Thus to the the Metamachine appears as an
ordinary GTP engine.

   Usage: no arguments gives normal GTP behavior.  `metamachine
--debug' sends diagnostics to stderr.

19.4.2 GNU Go as a Metamachine
------------------------------

Alternatively, you may compile GNU Go with the configure option
`--enable-metamachine'. This causes the file `oracle.c' to be compiled,
which contains the Metamachine code. This has no effect on the engine
unless you run GNU Go with the runtime option `--metamachine'. Thus you
must use both the configure and the runtime option to get the
Metamachine.

   This method is better than the standalone program since you have
access to GNU Go's facilities. For example, you can run the Metamachine
with CGoban or in Ascii mode this way.

   You can get traces by adding the command line `-d0x1000000'. In
debugging the Metamachine, a danger is that any small oversight in
designing the program can cause the forked process and the controller
to hang, each one waiting for a response from the other. If this seems
to happen it is useful to know that you can attach `gdb' to a running
process and find out what it is doing.

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File: gnugo.info,  Node: Adding new GTP commands,  Next: GTP command reference,  Prev: The Metamachine,  Up: GTP

19.5 Adding new GTP commands
============================

The implementation of GTP in GNU Go is distributed over three files,
`interface/gtp.h', `interface/gtp.c', and `interface/play_gtp.c'. The
first two implement a small library of helper functions which can be
used also by other programs. In the interest of promoting the GTP they
are licensed with minimal restrictions (*note GTP License::). The
actual GTP commands are implemented in `play_gtp.c', which has
knowledge about the engine internals.

   To see how a simple but fairly typical command is implemented we
look at `gtp_countlib()' (a GNU Go private extension command):

     static int
     gtp_countlib(char *s)
     {
       int i, j;
       if (!gtp_decode_coord(s, &i, &j))
         return gtp_failure("invalid coordinate");

       if (BOARD(i, j) == EMPTY)
         return gtp_failure("vertex must not be empty");

       return gtp_success("%d", countlib(POS(i, j)));
     }

   The arguments to the command are passed in the string `s'. In this
case we expect a vertex as argument and thus try to read it with
`gtp_decode_coord()' from `gtp.c'.

   A correctly formatted response should start with either `=' or `?',
followed by the identity number (if one was sent), the actual result,
and finally two consecutive newlines. It is important to get this
formatting correct since the controller in the other end relies on it.
Naturally the result itself cannot contain two consecutive newlines but
it may be split over several lines by single newlines.

   The easiest way to generate a correctly formatted response is with
one of the functions `gtp_failure()' and `gtp_success()', assuming that
their formatted output does not end with a newline.

   Sometimes the output is too complex for use with gtp_success, e.g. if
we want to print vertices, which gtp_success() does not support. Then
we have to fall back to the construction in e.g.  `gtp_genmove()':

     static int
     gtp_genmove(char *s)
     {
       [...]
       gtp_start_response(GTP_SUCCESS);
       gtp_print_vertex(i, j);
       return gtp_finish_response();
     }

   Here `gtp_start_response()' writes the equal sign and the identity
number while `gtp_finish_response()' adds the final two newlines.  The
next example is from `gtp_list_commands()':

     static int
     gtp_list_commands(char *s)
     {
       int k;
       UNUSED(s);

       gtp_start_response(GTP_SUCCESS);

       for (k = 0; commands[k].name != NULL; k++)
         gtp_printf("%s\n", commands[k].name);

       gtp_printf("\n");
       return GTP_OK;
     }

   As we have said, the response should be finished with two newlines.
Here we have to finish up the response ourselves since we already have
one newline in place from the last command printed in the loop.

   In order to add a new GTP command to GNU Go, the following pieces of
code need to be inserted in `play_gtp.c':
  1. A function declaration using the `DECLARE' macro in the list
     starting at line 68.

  2. An entry in the `commands[]' array starting at line 200.

  3. An implementation of the function handling the command.

   Useful helper functions in `gtp.c'/`gtp.h' are:
   * `gtp_printf()' for basic formatted printing.

   * `gtp_mprintf()' for printing with special format codes for
     vertices and colors.

   * `gtp_success()' and `gtp_failure()' for simple responses.

   * `gtp_start_response()' and `gtp_end_response()' for more complex
     responses.

   * `gtp_print_vertex()' and `gtp_print_vertices()' for printing one
     or multiple vertices.

   * `gtp_decode_color()' to read in a color from the command arguments.

   * `gtp_decode_coord()' to read in a vertex from the command
     arguments.

   * `gtp_decode_move()' to read in a move, i.e. color plus vertex,
     from the command arguments.

\1f
File: gnugo.info,  Node: GTP command reference,  Prev: Adding new GTP commands,  Up: GTP

19.6 GTP command reference
==========================

This section lists the GTP commands implemented in GNU Go along with
some information about each command. Each entry in the list has the
following fields:

   * Function: What this command does.

   * Arguments: What other information, if any, this command requires.
     Typical values include "none" or "vertex" or "integer" (there are
     others).

   * Fails: Circumstances which cause this command to fail.

   * Returns: What is displayed after the "=" and before the two
     newlines.  Typical values include "nothing" or "a move coordinate"
     or some status string (there are others).

   * Status: How this command relates to the standard GTP version 2
     commands. If nothing else is specified it is a GNU Go private
     extension.

   Without further ado, here is the big list (in no particular order).

   Note: if new commands are added by editing `interface/play_gtp.c'
this list could become incomplete. You may rebuild this list in
`doc/gtp-commands.texi' with the command `make gtp-commands' in the
`doc/' directory. This may require GNU sed.

   * quit: Quit
     Arguments: none
     Fails:     never
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * protocol_version: Report protocol version.
     Arguments: none
     Fails:     never
     Returns:   protocol version number

     Status:    GTP version 2 standard command.
      

   * name: Report the name of the program.
     Arguments: none
     Fails:     never
     Returns:   program name

     Status:    GTP version 2 standard command.
      

   * version: Report the version number of the program.
     Arguments: none
     Fails:     never
     Returns:   version number

     Status:    GTP version 2 standard command.
      

   * boardsize: Set the board size to NxN and clear the board.
     Arguments: integer
     Fails:     board size outside engine's limits
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * query_boardsize: Find the current boardsize
     Arguments: none
     Fails:     never
     Returns:   board_size
      

   * clear_board: Clear the board.
     Arguments: none
     Fails:     never
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * orientation: Set the orienation to N and clear the board
     Arguments: integer
     Fails:     illegal orientation
     Returns:   nothing
      

   * query_orientation: Find the current orientation
     Arguments: none
     Fails:     never
     Returns:   orientation
      

   * komi: Set the komi.
     Arguments: float
     Fails:     incorrect argument
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * get_komi: Get the komi
     Arguments: none
     Fails:     never
     Returns:   Komi
      

   * black: Play a black stone at the given vertex.
     Arguments: vertex
     Fails:     invalid vertex, illegal move
     Returns:   nothing

     Status:    Obsolete GTP version 1 command.
      

   * playwhite: Play a white stone at the given vertex.
     Arguments: vertex
     Fails:     invalid vertex, illegal move
     Returns:   nothing

     Status:    Obsolete GTP version 1 command.
      

   * play: Play a stone of the given color at the given vertex.
     Arguments: color, vertex
     Fails:     invalid vertex, illegal move
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * fixed_handicap: Set up fixed placement handicap stones.
     Arguments: number of handicap stones
     Fails:     invalid number of stones for the current boardsize
     Returns:   list of vertices with handicap stones

     Status:    GTP version 2 standard command.
      

   * place_free_handicap: Choose free placement handicap stones and put
     them on the board.
     Arguments: number of handicap stones
     Fails:     invalid number of stones
     Returns:   list of vertices with handicap stones

     Status:    GTP version 2 standard command.
      

   * set_free_handicap: Put free placement handicap stones on the board.
     Arguments: list of vertices with handicap stones
     Fails:     board not empty, bad list of vertices
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * get_handicap: Get the handicap
     Arguments: none
     Fails:     never
     Returns:   handicap
      

   * loadsgf: Load an sgf file, possibly up to a move number or the
     first occurence of a move.
     Arguments: filename + move number, vertex, or nothing
     Fails:     missing filename or failure to open or parse file
     Returns:   color to play

     Status:    GTP version 2 standard command.
      

   * color: Return the color at a vertex.
     Arguments: vertex
     Fails:     invalid vertex
     Returns:   "black", "white", or "empty"
      

   * list_stones: List vertices with either black or white stones.
     Arguments: color
     Fails:     invalid color
     Returns:   list of vertices
      

   * countlib: Count number of liberties for the string at a vertex.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   Number of liberties.
      

   * findlib: Return the positions of the liberties for the string at a
     vertex.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   Sorted space separated list of vertices.
      

   * accuratelib: Determine which liberties a stone of given color will
     get if played at given vertex.
     Arguments: move (color + vertex)
     Fails:     invalid color, invalid vertex, occupied vertex
     Returns:   Sorted space separated list of liberties
      

   * accurate_approxlib: Determine which liberties a stone of given
     color will get if played at given vertex.
     Arguments: move (color + vertex)
     Fails:     invalid color, invalid vertex, occupied vertex
     Returns:   Sorted space separated list of liberties

     Supposedly identical in behavior to the above function and
     can be retired when this is confirmed.
      

   * is_legal: Tell whether a move is legal.
     Arguments: move
     Fails:     invalid move
     Returns:   1 if the move is legal, 0 if it is not.
      

   * all_legal: List all legal moves for either color.
     Arguments: color
     Fails:     invalid color
     Returns:   Sorted space separated list of vertices.
      

   * captures: List the number of captures taken by either color.
     Arguments: color
     Fails:     invalid color
     Returns:   Number of captures.
      

   * last_move: Return the last move.
     Arguments: none
     Fails:     no previous move known
     Returns:   Color and vertex of last move.
      

   * move_history: Print the move history in reverse order
     Arguments: none
     Fails:     never
     Returns:   List of moves played in reverse order in format:
                color move (one move per line)
      

   * invariant_hash: Return the rotation/reflection invariant board
     hash.
     Arguments: none
     Fails:     never
     Returns:   Invariant hash for the board as a hexadecimal number.
      

   * invariant_hash_for_moves: Return the rotation/reflection invariant
     board hash obtained by playing all the possible moves for the
          given color.
     Arguments: color
     Fails:     invalid color
     Returns:   List of moves + invariant hash as a hexadecimal number,
                one pair of move + hash per line.
      

   * trymove: Play a stone of the given color at the given vertex.
     Arguments: move (color + vertex)
     Fails:     invalid color, invalid vertex, illegal move
     Returns:   nothing
      

   * tryko: Play a stone of the given color at the given vertex,
     allowing illegal ko capture.
     Arguments: move (color + vertex)
     Fails:     invalid color, invalid vertex, illegal move
     Returns:   nothing
      

   * popgo: Undo a trymove or tryko.
     Arguments: none
     Fails:     stack empty
     Returns:   nothing

   * clear_cache: clear the caches.
     Arguments: none.
     Fails:     never.
     Returns:   nothing.
      

   * attack: Try to attack a string.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   attack code followed by attack point if attack code nonzero.
      

   * attack_either: Try to attack either of two strings
     Arguments: two vertices
     Fails:     invalid vertex, empty vertex
     Returns:   attack code against the strings.  Guarantees there
                exists a move which will attack one of the two
                with attack_code, but does not return the move.
      

   * defend: Try to defend a string.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   defense code followed by defense point if defense code nonzero.
      

   * does_attack: Examine whether a specific move attacks a string
     tactically.
     Arguments: vertex (move), vertex (dragon)
     Fails:     invalid vertex, empty vertex
     Returns:   attack code
      

   * does_defend: Examine whether a specific move defends a string
     tactically.
     Arguments: vertex (move), vertex (dragon)
     Fails:     invalid vertex, empty vertex
     Returns:   attack code
      

   * ladder_attack: Try to attack a string strictly in a ladder.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   attack code followed by attack point if attack code nonzero.
      

   * increase_depths: Increase depth values by one.
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * decrease_depths: Decrease depth values by one.
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * owl_attack: Try to attack a dragon.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   attack code followed by attack point if attack code nonzero.
      

   * owl_defend: Try to defend a dragon.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   defense code followed by defense point if defense code nonzero.
      

   * owl_threaten_attack: Try to attack a dragon in 2 moves.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   attack code followed by the two attack points if
                attack code nonzero.
      

   * owl_threaten_defense: Try to defend a dragon with 2 moves.
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   defense code followed by the 2 defense points if
                defense code nonzero.
      

   * owl_does_attack: Examine whether a specific move attacks a dragon.
     Arguments: vertex (move), vertex (dragon)
     Fails:     invalid vertex, empty vertex
     Returns:   attack code
      

   * owl_does_defend: Examine whether a specific move defends a dragon.
     Arguments: vertex (move), vertex (dragon)
     Fails:     invalid vertex, empty vertex
     Returns:   defense code
      

   * owl_connection_defends: Examine whether a connection defends
     involved dragons.
     Arguments: vertex (move), vertex (dragon1), vertex (dragon2)
     Fails:     invalid vertex, empty vertex
     Returns:   defense code
      

   * defend_both: Try to defend both of two strings
     Arguments: two vertices
     Fails:     invalid vertex, empty vertex
     Returns:   defend code for the strings.  Guarantees there
                exists a move which will defend both of the two
                with defend_code, but does not return the move.
      

   * owl_substantial: Determine whether capturing a string gives a
     living dragon
     Arguments: vertex
     Fails:     invalid vertex, empty vertex
     Returns:   1 if dragon can live, 0 otherwise
      

   * analyze_semeai: Analyze a semeai
     Arguments: dragona, dragonb
     Fails:     invalid vertices, empty vertices
     Returns:   semeai defense result, semeai attack result, semeai move
      

   * analyze_semeai_after_move: Analyze a semeai after a move have been
     made.
     Arguments: color, vertex, dragona, dragonb
     Fails:     invalid vertices
     Returns:   semeai defense result, semeai attack result, semeai move
      

   * tactical_analyze_semeai: Analyze a semeai, not using owl
     Arguments: dragona, dragonb
     Fails:     invalid vertices, empty vertices
     Returns:   status of dragona, dragonb assuming dragona moves first
      

   * connect: Try to connect two strings.
     Arguments: vertex, vertex
     Fails:     invalid vertex, empty vertex, vertices of different colors
     Returns:   connect result followed by connect point if successful.
      

   * disconnect: Try to disconnect two strings.
     Arguments: vertex, vertex
     Fails:     invalid vertex, empty vertex, vertices of different colors
     Returns:   disconnect result followed by disconnect point if successful.
      

   * break_in: Try to break from string into area.
     Arguments: vertex, vertices
     Fails:     invalid vertex, empty vertex.
     Returns:   result followed by break in point if successful.
      

   * block_off: Try to block string from area.
     Arguments: vertex, vertices
     Fails:     invalid vertex, empty vertex.
     Returns:   result followed by block point if successful.

   * eval_eye: Evaluate an eye space
     Arguments: vertex
     Fails:     invalid vertex
     Returns:   Minimum and maximum number of eyes. If these differ an
                attack and a defense point are additionally returned.
                If the vertex is not an eye space or not of unique color,
                a single -1 is returned.

   * dragon_status: Determine status of a dragon.
     Arguments: optional vertex
     Fails:     invalid vertex, empty vertex
     Returns:   status ("alive", "critical", "dead", or "unknown"),
                attack point, defense point. Points of attack and
                defense are only given if the status is critical.
                If no vertex is given, the status is listed for all
                dragons, one per row in the format "A4: alive".

     FIXME: Should be able to distinguish between life in seki
            and independent life. Should also be able to identify ko.

   * same_dragon: Determine whether two stones belong to the same
     dragon.
     Arguments: vertex, vertex
     Fails:     invalid vertex, empty vertex
     Returns:   1 if the vertices belong to the same dragon, 0 otherwise

   * unconditional_status: Determine the unconditional status of a
     vertex.
     Arguments: vertex
     Fails:     invalid vertex
     Returns:   unconditional status ("undecided", "alive", "dead",
                "white_territory", "black_territory"). Occupied vertices can
                be undecided, alive, or dead. Empty vertices can be
                undecided, white territory, or black territory.

   * combination_attack: Find a move by color capturing something
     through a combination attack.
     Arguments: color
     Fails:     invalid color
     Returns:   Recommended move, PASS if no move found

   * combination_defend: If color can capture something through a
     combination attack, list moves by the opponent of color
     to defend against this attack.
     Arguments: color
     Fails:     invalid color
     Returns:   Recommended moves, PASS if no combination attack found.

   * aa_confirm_safety: Run atari_atari_confirm_safety().
     Arguments: move, optional int
     Fails:     invalid move
     Returns:   success code, if failure also defending move
      

   * genmove_black: Generate and play the supposedly best black move.
     Arguments: none
     Fails:     never
     Returns:   a move coordinate or "PASS"

     Status:    Obsolete GTP version 1 command.
      

   * genmove_white: Generate and play the supposedly best white move.
     Arguments: none
     Fails:     never
     Returns:   a move coordinate or "PASS"

     Status:    Obsolete GTP version 1 command.
      

   * genmove: Generate and play the supposedly best move for either
     color.
     Arguments: color to move
     Fails:     invalid color
     Returns:   a move coordinate or "PASS" (or "resign" if resignation_allowed)

     Status:    GTP version 2 standard command.
      

   * reg_genmove: Generate the supposedly best move for either color.
     Arguments: color to move
     Fails:     invalid color
     Returns:   a move coordinate (or "PASS")

     Status:    GTP version 2 standard command.
      

   * gg_genmove: Generate the supposedly best move for either color.
     Arguments: color to move, optionally a random seed
     Fails:     invalid color
     Returns:   a move coordinate (or "PASS")

     This differs from reg_genmove in the optional random seed.
      

   * restricted_genmove: Generate the supposedly best move for either
     color from a choice of allowed vertices.
     Arguments: color to move, allowed vertices
     Fails:     invalid color, invalid vertex, no vertex listed
     Returns:   a move coordinate (or "PASS")
      

   * kgs-genmove_cleanup: Generate and play the supposedly best move
     for either color, not passing until all dead opponent stones have
     been removed.
     Arguments: color to move
     Fails:     invalid color
     Returns:   a move coordinate (or "PASS")

     Status:    KGS specific command.

     A similar command, but possibly somewhat different, will likely be added
     to GTP version 3 at a later time.
      

   * level: Set the playing level.
     Arguments: int
     Fails:     incorrect argument
     Returns:   nothing

   * undo: Undo one move
     Arguments: none
     Fails:     If move history is too short.
     Returns:   nothing

     Status:    GTP version 2 standard command.

   * gg-undo: Undo a number of moves
     Arguments: optional int
     Fails:     If move history is too short.
     Returns:   nothing

   * time_settings: Set time allowance
     Arguments: int main_time, int byo_yomi_time, int byo_yomi_stones
     Fails:     syntax error
     Returns:   nothing

     Status:    GTP version 2 standard command.

   * time_left: Report remaining time
     Arguments: color color, int time, int stones
     Fails:     syntax error
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * final_score: Compute the score of a finished game.
     Arguments: Optional random seed
     Fails:     never
     Returns:   Score in SGF format (RE property).

     Status:    GTP version 2 standard command.
      

   * final_status: Report the final status of a vertex in a finished
     game.
     Arguments: Vertex, optional random seed
     Fails:     invalid vertex
     Returns:   Status in the form of one of the strings "alive", "dead",
                "seki", "white_territory", "black_territory", or "dame".
      

   * final_status_list: Report vertices with a specific final status in
     a finished game.
     Arguments: Status in the form of one of the strings "alive", "dead",
                "seki", "white_territory", "black_territory", or "dame".
                An optional random seed can be added.
     Fails:     missing or invalid status string
     Returns:   Vertices having the specified status. These are split with
                one string on each line if the vertices are nonempty (i.e.
                for "alive", "dead", and "seki").

     Status:    GTP version 2 standard command.
                However, "dame", "white_territory", and "black_territory"
                are private extensions.

   * estimate_score: Estimate the score
     Arguments: None
     Fails:     never
     Returns:   upper and lower bounds for the score

   * experimental_score: Estimate the score, taking into account which
     player moves next
     Arguments: Color to play
     Fails:     Invalid color
     Returns:   Score.

     This function generates a move for color, then adds the
     value of the move generated to the value of the position.
     Critical dragons are awarded to the opponent since the
     value of rescuing a critical dragon is taken into account
     in the value of the move generated.
      

   * reset_life_node_counter: Reset the count of life nodes.
     Arguments: none
     Fails:     never
     Returns:   nothing

     Note: This function is obsolete and only remains for backwards
     compatibility.
      

   * get_life_node_counter: Retrieve the count of life nodes.
     Arguments: none
     Fails:     never
     Returns:   number of life nodes

     Note: This function is obsolete and only remains for backwards
     compatibility.
      

   * reset_owl_node_counter: Reset the count of owl nodes.
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * get_owl_node_counter: Retrieve the count of owl nodes.
     Arguments: none
     Fails:     never
     Returns:   number of owl nodes
      

   * reset_reading_node_counter: Reset the count of reading nodes.
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * get_reading_node_counter: Retrieve the count of reading nodes.
     Arguments: none
     Fails:     never
     Returns:   number of reading nodes
      

   * reset_trymove_counter: Reset the count of trymoves/trykos.
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * get_trymove_counter: Retrieve the count of trymoves/trykos.
     Arguments: none
     Fails:     never
     Returns:   number of trymoves/trykos
      

   * reset_connection_node_counter: Reset the count of connection nodes.
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * get_connection_node_counter: Retrieve the count of connection
     nodes.
     Arguments: none
     Fails:     never
     Returns:   number of connection nodes
      

   * test_eyeshape: Test an eyeshape for inconsistent evaluations
     Arguments: Eyeshape vertices
     Fails:     Bad vertices
     Returns:   Failure reports on stderr.
      

   * analyze_eyegraph: Compute an eyevalue and vital points for an eye
     graph
     Arguments: Eyeshape encoded in string
     Fails:     Bad eyeshape, analysis failed
     Returns:   Eyevalue, vital points
      

   * cputime: Returns elapsed CPU time in seconds.
     Arguments: none
     Fails:     never
     Returns:   Total elapsed (user + system) CPU time in seconds.
      

   * showboard: Write the position to stdout.
     Arguments: none
     Fails:     never
     Returns:   nothing

     Status:    GTP version 2 standard command.
      

   * dump_stack: Dump stack to stderr.
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * initial_influence: Return information about the initial influence
     function.
     Arguments: color to move, what information
     Fails:     never
     Returns:   Influence data formatted like:

       0.51   1.34   3.20   6.60   9.09   8.06   1.96   0.00   0.00
       0.45   1.65   4.92  12.19  17.47  15.92   4.03   0.00   0.00
                       .
                       .
                       .
       0.00   0.00   0.00   0.00   0.00 100.00  75.53  41.47  23.41

     The available choices of information are:

     white_influence (float)
     black_influence (float)
     white_strength (float)
     black_strength (float)
     white_attenuation (float)
     black_attenuation (float)
     white_permeability (float)
     black_permeability (float)
     territory_value (float)
     influence_regions (int)
     non_territory (int)

     The encoding of influence_regions is as follows:
      4 white stone
      3 white territory
      2 white moyo
      1 white area
      0 neutral
     -1 black area
     -2 black moyo
     -3 black territory
     -4 black stone
      

   * move_influence: Return information about the influence function
     after a move.
     Arguments: move, what information
     Fails:     never
     Returns:   Influence data formatted like for initial_influence.
      

   * move_probabilities: List probabilities of each move being played
     (when non-zero). If no previous genmove command has been issued,
     the result            of this command will be meaningless.
     Arguments: none
     Fails:     never
     Returns:   Move, probabilty pairs, one per row.
      

   * move_uncertainty: Return the number of bits of uncertainty in the
     move. If no previous genmove command has been issued, the result
             of this command will be meaningless.
     Arguments: none
     Fails:     never
     Returns:   bits of uncertainty
      

   * followup_influence: Return information about the followup
     influence after a move.
     Arguments: move, what information
     Fails:     never
     Returns:   Influence data formatted like for initial_influence.
      

   * worm_data: Return the information in the worm data structure.
     Arguments: optional vertex
     Fails:     never
     Returns:   Worm data formatted like:

     A19:
     color           black
     size            10
     effective_size  17.83
     origin          A19
     liberties       8
     liberties2      15
     liberties3      10
     liberties4      8
     attack          PASS
     attack_code     0
     lunch           B19
     defend          PASS
     defend_code     0
     cutstone        2
     cutstone2       0
     genus           0
     inessential     0
     B19:
     color           white
     .
     .
     .
     inessential     0
     C19:
     ...

     If an intersection is specified, only data for this one will be returned.
      

   * worm_stones: List the stones of a worm
     Arguments: the location, "BLACK" or "WHITE"
     Fails:     if called on an empty or off-board location
     Returns:   list of stones
      

   * worm_cutstone: Return the cutstone field in the worm data
     structure.
     Arguments: non-empty vertex
     Fails:     never
     Returns:   cutstone
      

   * dragon_data: Return the information in the dragon data structure.
     Arguments: optional intersection
     Fails:     never
     Returns:   Dragon data formatted in the corresponding way to worm_data.
      

   * dragon_stones: List the stones of a dragon
     Arguments: the location
     Fails:     if called on an empty or off-board location
     Returns:   list of stones
      

   * eye_data: Return the information in the eye data structure.
     Arguments: color, vertex
     Fails:     never
     Returns:   eye data fields and values, one pair per row
      

   * half_eye_data: Return the information in the half eye data
     structure.
     Arguments: vertex
     Fails:     never
     Returns:   half eye data fields and values, one pair per row
      

   * start_sgftrace: Start storing moves executed during reading in an
     sgf tree in memory.
     Arguments: none
     Fails:     never
     Returns:   nothing

     Warning: You had better know what you're doing if you try to use this
              command.
      

   * finish_sgftrace: Finish storing moves in an sgf tree and write it
     to file.
     Arguments: filename
     Fails:     never
     Returns:   nothing

     Warning: You had better know what you're doing if you try to use this
              command.
      

   * printsgf: Dump the current position as a static sgf file to
     filename, or as output if filename is missing or "-"
     Arguments: optional filename
     Fails:     never
     Returns:   nothing if filename, otherwise the sgf
      

   * tune_move_ordering: Tune the parameters for the move ordering in
     the tactical reading.
     Arguments: MOVE_ORDERING_PARAMETERS integers
     Fails:     incorrect arguments
     Returns:   nothing
      

   * echo: Echo the parameter
     Arguments: string
     Fails:     never
     Returns:   nothing
      

   * echo_err: Echo the parameter to stdout AND stderr
     Arguments: string
     Fails:     never
     Returns:   nothing
      

   * help: List all known commands
     Arguments: none
     Fails:     never
     Returns:   list of known commands, one per line

     Status:    GTP version 2 standard command.
      

   * known_command: Tell whether a command is known.
     Arguments: command name
     Fails:     never
     Returns:   "true" if command exists, "false" if not

     Status:    GTP version 2 standard command.
      

   * report_uncertainty: Turn uncertainty reports from owl_attack and
     owl_defend on or off.
     Arguments: "on" or "off"
     Fails:     invalid argument
     Returns:   nothing
      

   * get_random_seed: Get the random seed
     Arguments: none
     Fails:     never
     Returns:   random seed
      

   * set_random_seed: Set the random seed
     Arguments: integer
     Fails:     invalid data
     Returns:   nothing
      

   * advance_random_seed: Advance the random seed by a number of games.
     Arguments: integer
     Fails:     invalid data
     Returns:   New random seed.
      

   * is_surrounded: Determine if a dragon is surrounded
     Arguments: vertex (dragon)
     Fails:     invalid vertex, empty vertex
     Returns:   1 if surrounded, 2 if weakly surrounded, 0 if not
      

   * does_surround: Determine if a move surrounds a dragon
     Arguments: vertex (move), vertex (dragon)
     Fails:     invalid vertex, empty (dragon, nonempty (move)
     Returns:   1 if (move) surrounds (dragon)

   * surround_map: Report the surround map for dragon at a vertex
     Arguments: vertex (dragon), vertex (mapped location)
     Fails:     invalid vertex, empty dragon
     Returns:   value of surround map at (mapped location), or -1 if
                dragon not surrounded.
      

   * set_search_diamond: limit search, and establish a search diamond
     Arguments: pos
     Fails:     invalid value
     Returns:   nothing
      

   * reset_search_mask: unmark the entire board for limited search
     Arguments: none
     Fails:     never
     Returns:   nothing
      

   * limit_search: sets the global variable limit_search
     Arguments: value
     Fails:     invalid arguments
     Returns:   nothing
      

   * set_search_limit: mark a vertex for limited search
     Arguments: position
     Fails:     invalid arguments
     Returns:   nothing
      

   * draw_search_area: Draw search area. Writes to stderr.
     Arguments: none
     Fails:     never
     Returns:   nothing

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File: gnugo.info,  Node: Regression,  Next: Copying,  Prev: GTP,  Up: Top

20 Regression testing
*********************

The standard purpose of regression testing is to avoid getting the same
bug twice. When a bug is found, the programmer fixes the bug and adds a
test to the test suite. The test should fail before the fix and pass
after the fix. When a new version is about to be released, all the tests
in the regression test suite are run and if an old bug reappears, this
will be seen quickly since the appropriate test will fail.

   The regression testing in GNU Go is slightly different. A typical
test case involves specifying a position and asking the engine what
move it would make. This is compared to one or more correct moves to
decide whether the test case passes or fails. It is also stored whether
a test case is expected to pass or fail, and deviations in this status
signify whether a change has solved some problem and/or broken something
else. Thus the regression tests both include positions highlighting some
mistake being done by the engine, which are waiting to be fixed, and
positions where the engine does the right thing, where we want to detect
if a change breaks something.

* Menu:

* Regression Testing::          Regression Testing in GNU Go
* Test Suites::                 Test Suites
* Running the Regressions::     Running the Regression Tests
* Running regress.pike::        Running regress.pike
* Viewing with Emacs::          Viewing tests with Emacs
* HTML Views::                  HTML Views

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File: gnugo.info,  Node: Regression Testing,  Next: Test Suites,  Up: Regression

20.1 Regression testing in GNU Go
=================================

Regression testing is performed by the files in the `regression/'
directory. The tests are specified as GTP commands in files with the
suffix `.tst', with corresponding correct results and expected
pass/fail status encoded in GTP comments following the test. To run a
test suite the shell scripts `test.sh', `eval.sh', and `regress.sh' can
be used. There are also Makefile targets to do this. If you `make
all_batches' most of the tests are run. The Pike script `regress.pike'
can also be used to run all tests or a subset of the tests.

   Game records used by the regression tests are stored in the
directory `regression/games/' and its subdirectories.

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File: gnugo.info,  Node: Test Suites,  Next: Running the Regressions,  Prev: Regression Testing,  Up: Regression

20.2 Test suites
================

The regression tests are grouped into suites and stored in files as GTP
commands. A part of a test suite can look as follows:
     # Connecting with ko at B14 looks best. Cutting at D17 might be
     # considered. B17 (game move) is inferior.
     loadsgf games/strategy25.sgf 61
     90 gg_genmove black
     #? [B14|D17]

     # The game move at P13 is a suicidal blunder.
     loadsgf games/strategy25.sgf 249
     95 gg_genmove black
     #? [!P13]

     loadsgf games/strategy26.sgf 257
     100 gg_genmove black
     #? [M16]*

   Lines starting with a hash sign, or in general anything following a
hash sign, are interpreted as comments by the GTP mode and thus ignored
by the engine. GTP commands are executed in the order they appear, but
only those on numbered lines are used for testing. The comment lines
starting with `#?' are magical to the regression testing scripts and
indicate correct results and expected pass/fail status. The string
within brackets is matched as a regular expression against the response
from the previous numbered GTP command. A particular useful feature of
regular expressions is that by using `|' it is possible to specify
alternatives. Thus `B14|D17' above means that if either `B14' or `D17'
is the move generated in test case 90, it passes. There is one
important special case to be aware of. If the correct result string
starts with an exclamation mark, this is excluded from the regular
expression but afterwards the result of the matching is negated. Thus
`!P13' in test case 95 means that any move except `P13' is accepted as
a correct result.

   In test case 100, the brackets on the `#?' line is followed by an
asterisk. This means that the test is expected to fail. If there is no
asterisk, the test is expected to pass. The brackets may also be
followed by a `&', meaning that the result is ignored. This is
primarily used to report statistics, e.g. how many tactical reading
nodes were spent while running the test suite.

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File: gnugo.info,  Node: Running the Regressions,  Next: Running regress.pike,  Prev: Test Suites,  Up: Regression

20.3 Running the Regression Tests
=================================

`./test.sh blunder.tst' runs the tests in `blunder.tst' and prints the
results of the commands on numbered lines, which may look like:

     1 E5
     2 F9
     3 O18
     4 B7
     5 A4
     6 E4
     7 E3
     8 A3
     9 D9
     10 J9
     11 B3
     12 C6
     13 C6

   This is usually not very informative, however. More interesting is
`./eval.sh blunder.tst' which also compares the results above against
the correct ones in the test file and prints a report for each test on
the form:

     1 failed: Correct '!E5', got 'E5'
     2 failed: Correct 'C9|H9', got 'F9'
     3 PASSED
     4 failed: Correct 'B5|C5|C4|D4|E4|E3|F3', got 'B7'
     5 PASSED
     6 failed: Correct 'D4', got 'E4'
     7 PASSED
     8 failed: Correct 'B4', got 'A3'
     9 failed: Correct 'G8|G9|H8', got 'D9'
     10 failed: Correct 'G9|F9|C7', got 'J9'
     11 failed: Correct 'D4|E4|E5|F4|C6', got 'B3'
     12 failed: Correct 'D4', got 'C6'
     13 failed: Correct 'D4|E4|E5|F4', got 'C6'

   The result of a test can be one of four different cases:

   * `passed': An expected pass

     This is the ideal result.

   * `PASSED': An unexpected pass

     This is a result that we are hoping for when we fix a bug. An old
     test case that used to fail is now passing.

   * `failed': An expected failure

     The test failed but this was also what we expected, unless we were
     trying to fix the particular mistake highlighted by the test case.
     These tests show weaknesses of the GNU Go engine and are good
     places to search if you want to detect an area which needs
     improvement.

   * `FAILED': An unexpected failure

     This should nominally only happen if something is broken by a
     change. However, sometimes GNU Go passes a test, but for the wrong
     reason or for a combination of wrong reasons.  When one of these
     reasons is fixed, the other one may shine through so that the test
     suddenly fails. When a test case unexpectedly fails, it is
     necessary to make a closer examination in order to determine
     whether a change has broken something.


   If you want a less verbose report, `./regress.sh . blunder.tst' does
the same thing as the previous command, but only reports unexpected
results. The example above is compressed to

     3 unexpected PASS!
     5 unexpected PASS!
     7 unexpected PASS!

   For convenience the tests are also available as makefile targets. For
example, `make blunder' runs the tests in the blunder test suite by
executing `eval.sh blunder.tst'. `make all_batches' runs all test
suites in a sequence using the `regress.sh' script.

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File: gnugo.info,  Node: Running regress.pike,  Next: Viewing with Emacs,  Prev: Running the Regressions,  Up: Regression

20.4 Running regress.pike
=========================

A more powerful way to run regressions is with the script
`regress.pike'. This requires that you have Pike
(`http://pike.ida.liu.se') installed.

   Executing `./regress.pike' without arguments will run all testsuites
that `make all_batches' would run. The difference is that unexpected
results are reported immediately when they have been found (instead of
after the whole file has been run) and that statistics of time
consumption and node usage is presented for each test file and in total.

   To run a single test suite do e.g. `./regress.pike nicklas3.tst' or
`./regress.pike nicklas3'. The result may look like:
     nicklas3                                 2.96    614772    3322      469
     Total nodes: 614772 3322 469
     Total time: 2.96 (3.22)
     Total uncertainty: 0.00
   The numbers here mean that the test suite took 2.96 seconds of
processor time and 3.22 seconds of real time. The consumption of
reading nodes was 614772 for tactical reading, 3322 for owl reading,
and 469 for connection reading. The last line relates to the
variability of the generated moves in the test suite, and 0 means that
none was decided by the randomness contribution to the move valuation.
Multiple testsuites can be run by e.g. `./regress.pike owl ld_owl owl1'.

   It is also possible to run a single testcase, e.g. `./regress.pike
strategy:6', a number of testcases, e.g. `./regress.pike
strategy:6,23,45', a range of testcases, e.g. `./regress.pike
strategy:13-15' or more complex combinations e.g. `./regress.pike
strategy:6,13-15,23,45 nicklas3:602,1403'.

   There are also command line options to choose what engine to run,
what options to send to the engine, to turn on verbose output, and to
use a file to specify which testcases to run. Run `./regress.pike
--help' for a complete and up to date list of options.

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File: gnugo.info,  Node: Viewing with Emacs,  Next: HTML Views,  Prev: Running regress.pike,  Up: Regression

20.5 Viewing tests with Emacs
=============================

To get a quick regression view, you may use the graphical display mode
available with Emacs (*note Emacs::). You will want the cursor in the
regression buffer when you enter `M-x gnugo', so that GNU Go opens in
the correct directory. A good way to be in the right directory is to
open the window of the test you want to investigate. Then you can cut
and past GTP commands directly from the test to the minibuffer, using
the `:' command from Emacs. Although Emacs mode does not have a
coordinate grid, you may get an ascii board with the coordinate grid
using `: showboard' command.

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File: gnugo.info,  Node: HTML Views,  Prev: Viewing with Emacs,  Up: Regression

20.6 HTML Regression Views
==========================

Extremely useful HTML Views of the regression tests may be produced
using two perl scripts `regression/regress.pl' and
`regression/regress.plx'.

  1. The driver program (regress.pl) which:
        * Runs the regression tests, invoking GNU Go.

        * Captures the trace output, board position, and pass/fail
          status, sgf output, and dragon status information.

  2. The interface to view the captured output (regress.plx) which:
        * Never invokes GNU Go.

        * Displays the captured output in helpful formats (i.e. HTML).

20.6.1 Setting up the HTML regression Views
-------------------------------------------

There are many ways configuring Apache to permit CGI scripts, all of
them are featured in Apache documentation, which can be found at
`http://httpd.apache.org/docs/2.0/howto/cgi.html'

   Below you will find one example.

   This documentation assumes an Apache 2.0 included in Fedora Core
distribution, but it should be fairly close to the config for other
distributions.

   First, you will need to configure Apache to run CGI scripts in the
directory you wish to serve the html views from. In
`/etc/httpd/conf/httpd.conf' there should be a line:

   `DocumentRoot "/var/www/html"'

   Search for a line `<Directory "/path/to/directory">', where
`/path/to/directory' is the same as provided in `DocumentRoot', then
add `ExecCGI' to list of `Options'.  The whole section should look like:

     <Directory "/var/www/html">
     ...
         Options ... ExecCGI
     ...
     </Directory>

   This allows CGI scripts to be executed in the directory used by
regress.plx.  Next, you need to tell Apache that `.plx' is a CGI script
ending. Your `httpd.conf' file should contain a line:

   `AddHandler cgi-script ...'

   If there isn't already, add it; add `.plx' to the list of extensions,
so line should look like:

   `AddHandler cgi-script ... .plx'

   You will also need to make sure you have the necessary modules
loaded to run CGI scripts; mod_cgi and mod_mime should be sufficient.
Your `httpd.conf' should have the relevant `LoadModule cgi_module
modules/mod_cgi.so' and `LoadModule mime_module modules/mod_mime.so'
lines; uncomment them if necessary.

   Next, you need to put a copy of `regress.plx' in the `DocumentRoot'
directory `/var/www/html' or it subdirectories where you plan to serve
the html views from.

   You will also need to install the Perl module GD
(`http://search.cpan.org/dist/GD/'), available from CPAN.

   Finally, run `regression/regress.pl' to create the xml data used to
generate the html views (to do all regression tests run
`regression/regress.pl -a 1'); then, copy the `html/' directory to the
same directory as `regress.plx' resides in.

   At this point, you should have a working copy of the html regression
views.

   Additional notes for Debian users: The Perl GD module can be
installed by `apt-get install libgd-perl'. It may suffice to add this to
the apache2 configuration:

     <Directory "/var/www/regression">
     	Options +ExecCGI
     	AddHandler cgi-script .plx
     	RedirectMatch ^/regression$ /regression/regress.plx
     </Directory>

   and then make a link from `/var/www/regression' to the GNU Go
regression directory. The `RedirectMatch' statement is only needed to
set up a shorter entry URL.

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File: gnugo.info,  Node: Copying,  Next: Concept Index,  Prev: Regression,  Up: Top

Appendix A Copying
******************

The program GNU Go is distributed under the terms of the GNU General
Public License (GPL). Its documentation is distributed under the terms
of the GNU Free Documentation License (GFDL).

* Menu:

* GPL::            The GNU General Public License
* GFDL::           The GNU Free Documentation License
* GTP License::    The Go Text Protocol License

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File: gnugo.info,  Node: GPL,  Next: GFDL,  Prev: Copying,  Up: Copying

A.1 GNU GENERAL PUBLIC LICENSE
==============================

                        Version 3, 29 June 2007

     Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

The GNU General Public License is a free, copyleft license for software
and other kinds of works.

   The licenses for most software and other practical works are designed
to take away your freedom to share and change the works.  By contrast,
the GNU General Public License is intended to guarantee your freedom to
share and change all versions of a program-to make sure it remains free
software for all its users.  We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to
any other work released this way by its authors.  You can apply it to
your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs, and that you know you can do these things.

   To protect your rights, we need to prevent others from denying you
these rights or asking you to surrender the rights.  Therefore, you have
certain responsibilities if you distribute copies of the software, or if
you modify it: responsibilities to respect the freedom of others.

   For example, if you distribute copies of such a program, whether
gratis or for a fee, you must pass on to the recipients the same
freedoms that you received.  You must make sure that they, too, receive
or can get the source code.  And you must show them these terms so they
know their rights.

   Developers that use the GNU GPL protect your rights with two steps:
(1) assert copyright on the software, and (2) offer you this License
giving you legal permission to copy, distribute and/or modify it.

   For the developers' and authors' protection, the GPL clearly explains
that there is no warranty for this free software.  For both users' and
authors' sake, the GPL requires that modified versions be marked as
changed, so that their problems will not be attributed erroneously to
authors of previous versions.

   Some devices are designed to deny users access to install or run
modified versions of the software inside them, although the manufacturer
can do so.  This is fundamentally incompatible with the aim of
protecting users' freedom to change the software.  The systematic
pattern of such abuse occurs in the area of products for individuals to
use, which is precisely where it is most unacceptable.  Therefore, we
have designed this version of the GPL to prohibit the practice for those
products.  If such problems arise substantially in other domains, we
stand ready to extend this provision to those domains in future versions
of the GPL, as needed to protect the freedom of users.

   Finally, every program is threatened constantly by software patents.
States should not allow patents to restrict development and use of
software on general-purpose computers, but in those that do, we wish to
avoid the special danger that patents applied to a free program could
make it effectively proprietary.  To prevent this, the GPL assures that
patents cannot be used to render the program non-free.

   The precise terms and conditions for copying, distribution and
modification follow.

                         TERMS AND CONDITIONS
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     "Copyright" also means copyright-like laws that apply to other
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     A separable portion of the object code, whose source code is
     excluded from the Corresponding Source as a System Library, need
     not be included in conveying the object code work.

     A "User Product" is either (1) a "consumer product", which means
     any tangible personal property which is normally used for
     personal, family, or household purposes, or (2) anything designed
     or sold for incorporation into a dwelling.  In determining whether
     a product is a consumer product, doubtful cases shall be resolved
     in favor of coverage.  For a particular product received by a
     particular user, "normally used" refers to a typical or common use
     of that class of product, regardless of the status of the
     particular user or of the way in which the particular user
     actually uses, or expects or is expected to use, the product.  A
     product is a consumer product regardless of whether the product
     has substantial commercial, industrial or non-consumer uses,
     unless such uses represent the only significant mode of use of the
     product.

     "Installation Information" for a User Product means any methods,
     procedures, authorization keys, or other information required to
     install and execute modified versions of a covered work in that
     User Product from a modified version of its Corresponding Source.
     The information must suffice to ensure that the continued
     functioning of the modified object code is in no case prevented or
     interfered with solely because modification has been made.

     If you convey an object code work under this section in, or with,
     or specifically for use in, a User Product, and the conveying
     occurs as part of a transaction in which the right of possession
     and use of the User Product is transferred to the recipient in
     perpetuity or for a fixed term (regardless of how the transaction
     is characterized), the Corresponding Source conveyed under this
     section must be accompanied by the Installation Information.  But
     this requirement does not apply if neither you nor any third party
     retains the ability to install modified object code on the User
     Product (for example, the work has been installed in ROM).

     The requirement to provide Installation Information does not
     include a requirement to continue to provide support service,
     warranty, or updates for a work that has been modified or
     installed by the recipient, or for the User Product in which it
     has been modified or installed.  Access to a network may be denied
     when the modification itself materially and adversely affects the
     operation of the network or violates the rules and protocols for
     communication across the network.

     Corresponding Source conveyed, and Installation Information
     provided, in accord with this section must be in a format that is
     publicly documented (and with an implementation available to the
     public in source code form), and must require no special password
     or key for unpacking, reading or copying.


  7. ADDITIONAL TERMS

     "Additional permissions" are terms that supplement the terms of
     this License by making exceptions from one or more of its
     conditions.  Additional permissions that are applicable to the
     entire Program shall be treated as though they were included in
     this License, to the extent that they are valid under applicable
     law.  If additional permissions apply only to part of the Program,
     that part may be used separately under those permissions, but the
     entire Program remains governed by this License without regard to
     the additional permissions.

     When you convey a copy of a covered work, you may at your option
     remove any additional permissions from that copy, or from any part
     of it.  (Additional permissions may be written to require their own
     removal in certain cases when you modify the work.)  You may place
     additional permissions on material, added by you to a covered work,
     for which you have or can give appropriate copyright permission.

     Notwithstanding any other provision of this License, for material
     you add to a covered work, you may (if authorized by the copyright
     holders of that material) supplement the terms of this License
     with terms:

     a) Disclaiming warranty or limiting liability differently from the
        terms of sections 15 and 16 of this License; or

     b) Requiring preservation of specified reasonable legal notices or
        author attributions in that material or in the Appropriate Legal
        Notices displayed by works containing it; or

     c) Prohibiting misrepresentation of the origin of that material, or
        requiring that modified versions of such material be marked in
       reasonable ways as different from the original version; or

     d) Limiting the use for publicity purposes of names of licensors or
        authors of the material; or

     e) Declining to grant rights under trademark law for use of some
      trade names, trademarks, or service marks; or

     f) Requiring indemnification of licensors and authors of that
     material by anyone who conveys the material (or modified versions
     of     it) with contractual assumptions of liability to the
     recipient, for     any liability that these contractual
     assumptions directly impose on     those licensors and authors.

     All other non-permissive additional terms are considered "further
     restrictions" within the meaning of section 10.  If the Program as
     you received it, or any part of it, contains a notice stating that
     it is governed by this License along with a term that is a further
     restriction, you may remove that term.  If a license document
     contains a further restriction but permits relicensing or
     conveying under this License, you may add to a covered work
     material governed by the terms of that license document, provided
     that the further restriction does not survive such relicensing or
     conveying.

     If you add terms to a covered work in accord with this section, you
     must place, in the relevant source files, a statement of the
     additional terms that apply to those files, or a notice indicating
     where to find the applicable terms.

     Additional terms, permissive or non-permissive, may be stated in
     the form of a separately written license, or stated as exceptions;
     the above requirements apply either way.


  8. TERMINATION

     You may not propagate or modify a covered work except as expressly
     provided under this License.  Any attempt otherwise to propagate or
     modify it is void, and will automatically terminate your rights
     under this License (including any patent licenses granted under
     the third paragraph of section 11).

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly and
     finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from
     you under this License.  If your rights have been terminated and
     not permanently reinstated, you do not qualify to receive new
     licenses for the same material under section 10.


  9. ACCEPTANCE NOT REQUIRED FOR HAVING COPIES

     You are not required to accept this License in order to receive or
     run a copy of the Program.  Ancillary propagation of a covered work
     occurring solely as a consequence of using peer-to-peer
     transmission to receive a copy likewise does not require
     acceptance.  However, nothing other than this License grants you
     permission to propagate or modify any covered work.  These actions
     infringe copyright if you do not accept this License.  Therefore,
     by modifying or propagating a covered work, you indicate your
     acceptance of this License to do so.


 10. AUTOMATIC LICENSING OF DOWNSTREAM RECIPIENTS

     Each time you convey a covered work, the recipient automatically
     receives a license from the original licensors, to run, modify and
     propagate that work, subject to this License.  You are not
     responsible for enforcing compliance by third parties with this
     License.

     An "entity transaction" is a transaction transferring control of an
     organization, or substantially all assets of one, or subdividing an
     organization, or merging organizations.  If propagation of a
     covered work results from an entity transaction, each party to that
     transaction who receives a copy of the work also receives whatever
     licenses to the work the party's predecessor in interest had or
     could give under the previous paragraph, plus a right to
     possession of the Corresponding Source of the work from the
     predecessor in interest, if the predecessor has it or can get it
     with reasonable efforts.

     You may not impose any further restrictions on the exercise of the
     rights granted or affirmed under this License.  For example, you
     may not impose a license fee, royalty, or other charge for
     exercise of rights granted under this License, and you may not
     initiate litigation (including a cross-claim or counterclaim in a
     lawsuit) alleging that any patent claim is infringed by making,
     using, selling, offering for sale, or importing the Program or any
     portion of it.


 11. PATENTS

     A "contributor" is a copyright holder who authorizes use under this
     License of the Program or a work on which the Program is based.
     The work thus licensed is called the contributor's "contributor
     version".

     A contributor's "essential patent claims" are all patent claims
     owned or controlled by the contributor, whether already acquired or
     hereafter acquired, that would be infringed by some manner,
     permitted by this License, of making, using, or selling its
     contributor version, but do not include claims that would be
     infringed only as a consequence of further modification of the
     contributor version.  For purposes of this definition, "control"
     includes the right to grant patent sublicenses in a manner
     consistent with the requirements of this License.

     Each contributor grants you a non-exclusive, worldwide,
     royalty-free patent license under the contributor's essential
     patent claims, to make, use, sell, offer for sale, import and
     otherwise run, modify and propagate the contents of its
     contributor version.

     In the following three paragraphs, a "patent license" is any
     express agreement or commitment, however denominated, not to
     enforce a patent (such as an express permission to practice a
     patent or covenant not to sue for patent infringement).  To
     "grant" such a patent license to a party means to make such an
     agreement or commitment not to enforce a patent against the party.

     If you convey a covered work, knowingly relying on a patent
     license, and the Corresponding Source of the work is not available
     for anyone to copy, free of charge and under the terms of this
     License, through a publicly available network server or other
     readily accessible means, then you must either (1) cause the
     Corresponding Source to be so available, or (2) arrange to deprive
     yourself of the benefit of the patent license for this particular
     work, or (3) arrange, in a manner consistent with the requirements
     of this License, to extend the patent license to downstream
     recipients.  "Knowingly relying" means you have actual knowledge
     that, but for the patent license, your conveying the covered work
     in a country, or your recipient's use of the covered work in a
     country, would infringe one or more identifiable patents in that
     country that you have reason to believe are valid.

     If, pursuant to or in connection with a single transaction or
     arrangement, you convey, or propagate by procuring conveyance of, a
     covered work, and grant a patent license to some of the parties
     receiving the covered work authorizing them to use, propagate,
     modify or convey a specific copy of the covered work, then the
     patent license you grant is automatically extended to all
     recipients of the covered work and works based on it.

     A patent license is "discriminatory" if it does not include within
     the scope of its coverage, prohibits the exercise of, or is
     conditioned on the non-exercise of one or more of the rights that
     are specifically granted under this License.  You may not convey a
     covered work if you are a party to an arrangement with a third
     party that is in the business of distributing software, under
     which you make payment to the third party based on the extent of
     your activity of conveying the work, and under which the third
     party grants, to any of the parties who would receive the covered
     work from you, a discriminatory patent license (a) in connection
     with copies of the covered work conveyed by you (or copies made
     from those copies), or (b) primarily for and in connection with
     specific products or compilations that contain the covered work,
     unless you entered into that arrangement, or that patent license
     was granted, prior to 28 March 2007.

     Nothing in this License shall be construed as excluding or limiting
     any implied license or other defenses to infringement that may
     otherwise be available to you under applicable patent law.


 12. NO SURRENDER OF OTHERS' FREEDOM

     If conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot convey a covered work so as to satisfy
     simultaneously your obligations under this License and any other
     pertinent obligations, then as a consequence you may not convey it
     at all.  For example, if you agree to terms that obligate you to
     collect a royalty for further conveying from those to whom you
     convey the Program, the only way you could satisfy both those
     terms and this License would be to refrain entirely from conveying
     the Program.


 13. USE WITH THE GNU AFFERO GENERAL PUBLIC LICENSE

     Notwithstanding any other provision of this License, you have
     permission to link or combine any covered work with a work licensed
     under version 3 of the GNU Affero General Public License into a
     single combined work, and to convey the resulting work.  The terms
     of this License will continue to apply to the part which is the
     covered work, but the special requirements of the GNU Affero
     General Public License, section 13, concerning interaction through
     a network will apply to the combination as such.


 14. REVISED VERSIONS OF THIS LICENSE

     The Free Software Foundation may publish revised and/or new
     versions of the GNU General Public License from time to time.
     Such new versions will be similar in spirit to the present
     version, but may differ in detail to address new problems or
     concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies that a certain numbered version of the GNU
     General Public License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that numbered version or of any later version published by the
     Free Software Foundation.  If the Program does not specify a
     version number of the GNU General Public License, you may choose
     any version ever published by the Free Software Foundation.

     If the Program specifies that a proxy can decide which future
     versions of the GNU General Public License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Program.

     Later license versions may give you additional or different
     permissions.  However, no additional obligations are imposed on any
     author or copyright holder as a result of your choosing to follow a
     later version.


 15. DISCLAIMER OF WARRANTY

     THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
     APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE
     COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
     WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE
     RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.
     SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
     NECESSARY SERVICING, REPAIR OR CORRECTION.


 16. LIMITATION OF LIABILITY.

     IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
     AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU
     FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
     CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
     THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
     BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
     PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
     PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
     THE POSSIBILITY OF SUCH DAMAGES.


 17. INTERPRETATION OF SECTIONS 15 AND 16

     If the disclaimer of warranty and limitation of liability provided
     above cannot be given local legal effect according to their terms,
     reviewing courts shall apply local law that most closely
     approximates an absolute waiver of all civil liability in
     connection with the Program, unless a warranty or assumption of
     liability accompanies a copy of the Program in return for a fee.


How to Apply These Terms to your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.

   <one line to give the program's name and a brief idea of what it
does.>     Copyright (C) <year>  <name of author>

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

   This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the     GNU
General Public License for more details.

   You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

   Also add information on how to contact you by electronic and paper
mail.

   If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

   <program>  Copyright (C) <year>  <name of author>     This program
comes with ABSOLUTELY NO WARRANTY; for details type `show w'.      This
is free software, and you are welcome to redistribute it     under
certain conditions; type `show c' for details.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".

   You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  For more information on this, and how to apply and follow
the GNU GPL, see <http://www.gnu.org/licenses/>.

   The GNU General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Lesser General Public License instead of this License.  But first,
please read <http://www.gnu.org/philosophy/why-not-lgpl.html>.

\1f
File: gnugo.info,  Node: GFDL,  Next: GTP License,  Prev: GPL,  Up: Copying

A.2 GNU FREE DOCUMENTATION LICENSE
==================================

                     Version 1.3, 3 November 2008

     Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     `http://fsf.org/'

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.
     We recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it
     can be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You
     accept the license if you copy, modify or distribute the work in a
     way requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in
     the notice that says that the Document is released under this
     License.  If a section does not fit the above definition of
     Secondary then it is not allowed to be designated as Invariant.
     The Document may contain zero Invariant Sections.  If the Document
     does not identify any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images
     composed of pixels) generic paint programs or (for drawings) some
     widely available drawing editor, and that is suitable for input to
     text formatters or for automatic translation to a variety of
     formats suitable for input to text formatters.  A copy made in an
     otherwise Transparent file format whose markup, or absence of
     markup, has been arranged to thwart or discourage subsequent
     modification by readers is not Transparent.  An image format is
     not Transparent if used for any substantial amount of text.  A
     copy that is not "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and
     standard-conforming simple HTML, PostScript or PDF designed for
     human modification.  Examples of transparent image formats include
     PNG, XCF and JPG.  Opaque formats include proprietary formats that
     can be read and edited only by proprietary word processors, SGML or
     XML for which the DTD and/or processing tools are not generally
     available, and the machine-generated HTML, PostScript or PDF
     produced by some word processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     The "publisher" means any person or entity that distributes copies
     of the Document to the public.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements", "Dedications", "Endorsements", or "History".)
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
     covers, as long as they preserve the title of the Document and
     satisfy these conditions, can be treated as verbatim copying in
     other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy a computer-network location from
     which the general network-using public has access to download
     using public-standard network protocols a complete Transparent
     copy of the Document, free of added material.  If you use the
     latter option, you must take reasonably prudent steps, when you
     begin distribution of Opaque copies in quantity, to ensure that
     this Transparent copy will remain thus accessible at the stated
     location until at least one year after the last time you
     distribute an Opaque copy (directly or through your agents or
     retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
     copies, to give them a chance to provide you with an updated
     version of the Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of
          previous versions (which should, if there were any, be listed
          in the History section of the Document).  You may use the
          same title as a previous version if the original publisher of
          that version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on
          the Title Page.  If there is no section Entitled "History" in
          the Document, create one stating the title, year, authors,
          and publisher of the Document as given on its Title Page,
          then add an item describing the Modified Version as stated in
          the previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
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ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.

\1f
File: gnugo.info,  Node: GTP License,  Prev: GFDL,  Up: Copying

A.3 The Go Text Protocol License
================================

In order to facilitate the use of the Go Text Protocol, the two files
`gtp.c' and `gtp.h' are licensed under the following terms.

   Copyright 2001 by the Free Software Foundation.

   Permission is hereby granted, free of charge, to any person
obtaining a copy of this file `gtp.x', to deal in the Software without
restriction, including without limitation the rights to use, copy,
modify, merge, publish, distribute, and/or sell copies of the Software,
and to permit persons to whom the Software is furnished to do so,
provided that the above copyright notice(s) and this permission notice
appear in all copies of the Software and that both the above copyright
notice(s) and this permission notice appear in supporting documentation.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
OF THIRD PARTY RIGHTS. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
HOLDERS INCLUDED IN THIS NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL
INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING
FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

   Except as contained in this notice, the name of a copyright holder
shall not be used in advertising or otherwise to promote the sale, use
or other dealings in this Software without prior written authorization
of the copyright holder.

\1f
File: gnugo.info,  Node: Concept Index,  Next: Functions Index,  Prev: Copying,  Up: Top

Concept Index
*************

\0\b[index\0\b]
* Menu:

* aa_confirm_safety:                     GTP command reference.
                                                             (line  492)
* accurate_approxlib:                    GTP command reference.
                                                             (line  207)
* accuratelib:                           GTP command reference.
                                                             (line  200)
* adjacent dragons:                      Dragons.            (line  145)
* advance_random_seed:                   GTP command reference.
                                                             (line  960)
* all_legal:                             GTP command reference.
                                                             (line  223)
* amalgamation of worms into dragons:    Amalgamation.       (line    6)
* analyze_eyegraph:                      GTP command reference.
                                                             (line  710)
* analyze_semeai:                        GTP command reference.
                                                             (line  400)
* analyze_semeai_after_move:             GTP command reference.
                                                             (line  406)
* API:                                   API.                (line   26)
* area:                                  Territory and Moyo. (line    6)
* ascii description of shapes:           Patterns Overview.  (line   27)
* ascii interface:                       Ascii.              (line    6)
* ascii mode:                            Invoking GNU Go.    (line  336)
* attack:                                GTP command reference.
                                                             (line  288)
* attack shapes database:                Patterns Overview.  (line    6)
* attack_either:                         GTP command reference.
                                                             (line  294)
* autohelper actions:                    Autohelper Actions. (line    6)
* Autohelpers:                           Autohelpers and Constraints.
                                                             (line    6)
* automaton:                             DFA.                (line   29)
* black:                                 GTP command reference.
                                                             (line  111)
* block_off:                             GTP command reference.
                                                             (line  437)
* board_state:                           The Board State.    (line    6)
* boardsize:                             GTP command reference.
                                                             (line   63)
* break_in:                              GTP command reference.
                                                             (line  431)
* cache:                                 Invoking GNU Go.    (line  119)
* cache-size:                            Invoking GNU Go.    (line  119)
* captures:                              GTP command reference.
                                                             (line  229)
* CGoban:                                CGoban.             (line    6)
* clear_board:                           GTP command reference.
                                                             (line   77)
* clear_cache:                           GTP command reference.
                                                             (line  284)
* color:                                 GTP command reference.
                                                             (line  175)
* color (dragon):                        Dragons.            (line   98)
* colored display <1>:                   Dragons in Color.   (line    6)
* colored display:                       Colored Display.    (line    6)
* combination_attack:                    GTP command reference.
                                                             (line  479)
* combination_defend:                    GTP command reference.
                                                             (line  485)
* command line options:                  Invoking GNU Go.    (line    6)
* connect:                               GTP command reference.
                                                             (line  419)
* connection shapes database <1>:        Connections Database.
                                                             (line    6)
* connection shapes database:            Patterns Overview.  (line    6)
* connections:                           Connection.         (line    6)
* connections database:                  Connections Database.
                                                             (line    6)
* corner matcher:                        Corner Matcher.     (line    6)
* countlib:                              GTP command reference.
                                                             (line  187)
* cputime:                               GTP command reference.
                                                             (line  717)
* cutting stone:                         Worms.              (line  124)
* cutting stone, potential:              Worms.              (line  133)
* data structures:                       Basic Data Structures.
                                                             (line    6)
* debugging on a graphical board:        view.pike.          (line    6)
* debugging options:                     Invoking GNU Go.    (line  415)
* Debugging the reading code:            Debugging.          (line    6)
* decide-dragon:                         Decide dragon.      (line    6)
* decide-string:                         Decide string.      (line    6)
* decrease_depths:                       GTP command reference.
                                                             (line  334)
* defence shapes database:               Patterns Overview.  (line    6)
* defend:                                GTP command reference.
                                                             (line  302)
* defend_both:                           GTP command reference.
                                                             (line  385)
* depth:                                 Invoking GNU Go.    (line  242)
* Depth of reading:                      Tactical Reading.   (line    6)
* description of shapes:                 Patterns Overview.  (line   27)
* dfa:                                   DFA.                (line   29)
* dfa.c:                                 DFA.                (line   29)
* dfa.h:                                 DFA.                (line   29)
* disconnect:                            GTP command reference.
                                                             (line  425)
* distance from liberty to dragon:       Worms.              (line  109)
* does_attack:                           GTP command reference.
                                                             (line  308)
* does_defend:                           GTP command reference.
                                                             (line  315)
* does_surround:                         GTP command reference.
                                                             (line  972)
* dragon:                                Worms and Dragons.  (line   27)
* dragon escape_route:                   Dragons.            (line  207)
* dragon genus:                          Dragons.            (line  213)
* dragon lunch:                          Dragons.            (line  230)
* dragon number:                         Dragons.            (line  100)
* dragon origin:                         Dragons.            (line  104)
* dragon safety:                         Dragons.            (line  176)
* dragon size:                           Dragons.            (line  112)
* dragon status:                         Dragons.            (line  131)
* dragon weakness:                       Dragons.            (line  199)
* dragon_data:                           GTP command reference.
                                                             (line  854)
* dragon_status:                         GTP command reference.
                                                             (line  452)
* dragon_stones:                         GTP command reference.
                                                             (line  860)
* dragons:                               Dragons.            (line    6)
* draw_search_area:                      GTP command reference.
                                                             (line 1008)
* dump_stack:                            GTP command reference.
                                                             (line  731)
* echo:                                  GTP command reference.
                                                             (line  913)
* echo_err:                              GTP command reference.
                                                             (line  919)
* editing pattern database:              Editing Patterns.   (line    6)
* editing patterns:                      Editing Patterns.   (line    6)
* effective size:                        Dragons.            (line  116)
* effective size (worm):                 Worms.              (line   48)
* eliminate the randomness:              Tuning.             (line  155)
* emacs mode:                            Emacs.              (line    6)
* escape_route:                          Dragons.            (line  207)
* estimate_score:                        GTP command reference.
                                                             (line  621)
* eval_eye:                              GTP command reference.
                                                             (line  444)
* experimental_score:                    GTP command reference.
                                                             (line  626)
* eye shapes database:                   Patterns Overview.  (line    6)
* eye space display:                     Colored Display.    (line   48)
* eye_data:                              GTP command reference.
                                                             (line  866)
* false eye:                             Half Eyes.          (line    6)
* fast pattern matching:                 DFA.                (line   29)
* final_score:                           GTP command reference.
                                                             (line  589)
* final_status:                          GTP command reference.
                                                             (line  597)
* final_status_list:                     GTP command reference.
                                                             (line  605)
* findlib:                               GTP command reference.
                                                             (line  193)
* finish_sgftrace:                       GTP command reference.
                                                             (line  889)
* finite state automaton:                DFA.                (line   29)
* fixed_handicap:                        GTP command reference.
                                                             (line  135)
* FIXME:                                 Coding Styles.      (line   83)
* followup_influence:                    GTP command reference.
                                                             (line  799)
* format of the pattern database:        Patterns Overview.  (line   27)
* formatted printing:                    Print Utilities.    (line    6)
* GDB <1>:                               Debugging.          (line   30)
* GDB:                                   GTP and GDB techniques.
                                                             (line    6)
* generation of helper functions:        Autohelpers and Constraints.
                                                             (line    6)
* genmove:                               GTP command reference.
                                                             (line  512)
* genmove_black:                         GTP command reference.
                                                             (line  496)
* genmove_white:                         GTP command reference.
                                                             (line  504)
* genus:                                 Dragons.            (line  213)
* genus (worm):                          Worms.              (line  155)
* get_connection_node_counter:           GTP command reference.
                                                             (line  697)
* get_handicap:                          GTP command reference.
                                                             (line  160)
* get_komi:                              GTP command reference.
                                                             (line  105)
* get_life_node_counter:                 GTP command reference.
                                                             (line  646)
* get_owl_node_counter:                  GTP command reference.
                                                             (line  661)
* get_random_seed:                       GTP command reference.
                                                             (line  948)
* get_reading_node_counter:              GTP command reference.
                                                             (line  673)
* get_trymove_counter:                   GTP command reference.
                                                             (line  685)
* gg-undo:                               GTP command reference.
                                                             (line  571)
* gg_genmove:                            GTP command reference.
                                                             (line  529)
* GMP:                                   GMP and GTP.        (line    6)
* GNU Go's GDB commands:                 Debugging.          (line   82)
* go position:                           Hash Calculation.   (line   10)
* grid optimization:                     Details.            (line    6)
* GTP <1>:                               GTP and GDB techniques.
                                                             (line    6)
* GTP:                                   GMP and GTP.        (line    6)
* GTP command reference:                 GTP command reference.
                                                             (line    6)
* half eye:                              Half Eyes.          (line    6)
* half_eye_data:                         GTP command reference.
                                                             (line  872)
* Hash node:                             Hash Organization.  (line    8)
* Hashing of positions:                  Hashing.            (line    6)
* help:                                  GTP command reference.
                                                             (line  925)
* helper functions in pattern matching:  Helper Functions.   (line    6)
* how GNU Go learns new joseki:          Joseki Compiler.    (line    6)
* How to debug the reading code:         Debugging.          (line    6)
* implementation of pattern matching <1>: Corner Matcher.    (line    6)
* implementation of pattern matching:    PM Implementation.  (line    6)
* increase_depths:                       GTP command reference.
                                                             (line  328)
* inessential string:                    Worms.              (line  165)
* initial_influence:                     GTP command reference.
                                                             (line  737)
* installation:                          GNU/Linux and Unix. (line    6)
* invariant_hash:                        GTP command reference.
                                                             (line  248)
* invariant_hash_for_moves:              GTP command reference.
                                                             (line  255)
* invincible worm:                       Worms.              (line  178)
* invoking GNU Go:                       Invoking GNU Go.    (line    6)
* is_legal:                              GTP command reference.
                                                             (line  217)
* is_surrounded:                         GTP command reference.
                                                             (line  966)
* jago:                                  Other Clients.      (line    6)
* joseki <1>:                            Corner Matcher.     (line    6)
* joseki:                                Joseki Compiler.    (line    6)
* kgs-genmove_cleanup:                   GTP command reference.
                                                             (line  544)
* known_command:                         GTP command reference.
                                                             (line  933)
* komi:                                  GTP command reference.
                                                             (line   97)
* ladder_attack:                         GTP command reference.
                                                             (line  322)
* last_move:                             GTP command reference.
                                                             (line  235)
* level <1>:                             GTP command reference.
                                                             (line  557)
* level:                                 Invoking GNU Go.    (line  225)
* level of play:                         Invoking GNU Go.    (line   25)
* liberties (worm):                      Worms.              (line   74)
* liberties, higher order (worm):        Worms.              (line   74)
* licence, documentation (GFDL):         GFDL.               (line    3)
* licence, program (GPL):                GPL.                (line    3)
* limit_search:                          GTP command reference.
                                                             (line  996)
* list_stones:                           GTP command reference.
                                                             (line  181)
* loadsgf:                               GTP command reference.
                                                             (line  166)
* lunch:                                 Dragons.            (line  230)
* lunch (worm):                          Worms.              (line  114)
* matchpat.c:                            DFA.                (line   29)
* Monte Carlo Go:                        Monte Carlo Go.     (line    6)
* move generation:                       Move Generators.    (line    6)
* move generators:                       Move Generators.    (line    6)
* move reasons <1>:                      Move Reasons.       (line    6)
* move reasons:                          Move Generators.    (line    6)
* move_history:                          GTP command reference.
                                                             (line  241)
* move_influence:                        GTP command reference.
                                                             (line  776)
* move_probabilities:                    GTP command reference.
                                                             (line  783)
* move_uncertainty:                      GTP command reference.
                                                             (line  791)
* moyo:                                  Territory and Moyo. (line    6)
* name:                                  GTP command reference.
                                                             (line   47)
* neighbor dragons:                      Dragons.            (line  145)
* orientation:                           GTP command reference.
                                                             (line   85)
* origin (worm):                         Worms.              (line   58)
* output file:                           Output File.        (line    6)
* owl_attack:                            GTP command reference.
                                                             (line  340)
* owl_attack_certain:                    Dragons.            (line  296)
* owl_attack_code:                       Dragons.            (line  291)
* owl_attack_point:                      Dragons.            (line  286)
* owl_connection_defends:                GTP command reference.
                                                             (line  378)
* owl_defend:                            GTP command reference.
                                                             (line  346)
* owl_defense_certain:                   Dragons.            (line  314)
* owl_defense_code:                      Dragons.            (line  309)
* owl_defense_point:                     Dragons.            (line  305)
* owl_does_attack:                       GTP command reference.
                                                             (line  366)
* owl_does_defend:                       GTP command reference.
                                                             (line  372)
* owl_second_attack_point:               Dragons.            (line  301)
* owl_second_defense_point:              Dragons.            (line  319)
* owl_substantial:                       GTP command reference.
                                                             (line  393)
* owl_threaten_attack:                   GTP command reference.
                                                             (line  352)
* owl_threaten_defense:                  GTP command reference.
                                                             (line  359)
* pattern attributes:                    Pattern Classification.
                                                             (line    6)
* pattern database <1>:                  DFA.                (line   29)
* pattern database:                      Patterns Overview.  (line    6)
* pattern matching <1>:                  DFA.                (line   29)
* pattern matching:                      Patterns Overview.  (line    6)
* pattern matching optimization:         Details.            (line    6)
* pattern overview:                      Patterns Overview.  (line    6)
* pattern.c:                             Patterns Overview.  (line    6)
* pattern.h:                             Patterns Overview.  (line    6)
* persistent cache:                      Persistent Cache.   (line    6)
* place_free_handicap:                   GTP command reference.
                                                             (line  143)
* play:                                  GTP command reference.
                                                             (line  127)
* playwhite:                             GTP command reference.
                                                             (line  119)
* popgo:                                 GTP command reference.
                                                             (line  277)
* position:                              Hash Calculation.   (line   10)
* position struct:                       Basic Data Structures.
                                                             (line    6)
* potential cutting stone:               Worms.              (line  133)
* printsgf:                              GTP command reference.
                                                             (line  899)
* product:                               DFA.                (line   29)
* protocol_version:                      GTP command reference.
                                                             (line   39)
* qGo:                                   Other Clients.      (line    6)
* quarry:                                Other Clients.      (line    6)
* query_boardsize:                       GTP command reference.
                                                             (line   71)
* query_orientation:                     GTP command reference.
                                                             (line   91)
* quit:                                  GTP command reference.
                                                             (line   33)
* Read result:                           Hash Organization.  (line    8)
* Reading code:                          Tactical Reading.   (line    6)
* Reading code debugging tools:          Debugging.          (line    6)
* reading DEPTH:                         Tactical Reading.   (line    6)
* Reading optimisation:                  Hashing.            (line    6)
* Reading process:                       Tactical Reading.   (line    6)
* reading return codes:                  Reading Basics.     (line   51)
* reading shadow:                        Persistent Cache.   (line   50)
* reading.c <1>:                         Reading Basics.     (line  122)
* reading.c:                             Tactical Reading.   (line    6)
* reading.h:                             Tactical Reading.   (line    6)
* reg_genmove:                           GTP command reference.
                                                             (line  521)
* report_uncertainty:                    GTP command reference.
                                                             (line  941)
* reset_connection_node_counter:         GTP command reference.
                                                             (line  691)
* reset_life_node_counter:               GTP command reference.
                                                             (line  637)
* reset_owl_node_counter:                GTP command reference.
                                                             (line  655)
* reset_reading_node_counter:            GTP command reference.
                                                             (line  667)
* reset_search_mask:                     GTP command reference.
                                                             (line  990)
* reset_trymove_counter:                 GTP command reference.
                                                             (line  679)
* restricted_genmove:                    GTP command reference.
                                                             (line  537)
* return codes:                          Reading Basics.     (line   51)
* same_dragon:                           GTP command reference.
                                                             (line  464)
* scoring:                               Scoring.            (line    6)
* semeai:                                Dragons.            (line  254)
* semeai_attack_certain:                 Dragons.            (line  254)
* semeai_attack_point:                   Dragons.            (line  254)
* semeai_defense_certain:                Dragons.            (line  254)
* semeai_defense_point:                  Dragons.            (line  254)
* set_free_handicap:                     GTP command reference.
                                                             (line  152)
* set_random_seed:                       GTP command reference.
                                                             (line  954)
* set_search_diamond:                    GTP command reference.
                                                             (line  984)
* set_search_limit:                      GTP command reference.
                                                             (line 1002)
* SGF (Smart Game Format):               SGF Support.        (line    6)
* SGF files in memory:                   SGF.                (line    6)
* shape attributes:                      Pattern Classification.
                                                             (line    6)
* showboard:                             GTP command reference.
                                                             (line  723)
* Smart Game Format:                     SGF Support.        (line    6)
* Speedup of reading process:            Hashing.            (line    6)
* start_sgftrace:                        GTP command reference.
                                                             (line  879)
* string:                                Worms and Dragons.  (line   27)
* superstring:                           General Utilities.  (line  249)
* surround:                              Dragons.            (line  238)
* surround_map:                          GTP command reference.
                                                             (line  979)
* surround_size:                         Dragons.            (line  238)
* surround_status:                       Dragons.            (line  238)
* symmetry and transformations:          Symmetry & transformations.
                                                             (line    6)
* symmetry and transformations of shapes: Symmetry & transformations.
                                                             (line    6)
* tactical_analyze_semeai:               GTP command reference.
                                                             (line  413)
* teaching josekis to GNU Go:            Joseki Compiler.    (line    6)
* territory:                             Territory and Moyo. (line    6)
* test_eyeshape:                         GTP command reference.
                                                             (line  704)
* The Go Modem Protocol and Go Text Protocol: GMP and GTP.   (line    6)
* the joseki compiler:                   Joseki Compiler.    (line    6)
* time_left:                             GTP command reference.
                                                             (line  583)
* time_settings:                         GTP command reference.
                                                             (line  576)
* timers:                                General Utilities.  (line  328)
* traces:                                Traces.             (line    6)
* Transposition table:                   Hashing.            (line    6)
* Trying hypothetical moves:             Tactical Reading.   (line    6)
* tryko:                                 GTP command reference.
                                                             (line  270)
* trymove:                               GTP command reference.
                                                             (line  264)
* tune_move_ordering:                    GTP command reference.
                                                             (line  906)
* tuning GNU Go:                         Traces.             (line    6)
* tuning the pattern database:           Tuning.             (line    6)
* tuning the shapes database:            Tuning.             (line    6)
* UCT algorithm:                         Monte Carlo Go.     (line    6)
* unconditional_status:                  GTP command reference.
                                                             (line  470)
* undo:                                  GTP command reference.
                                                             (line  564)
* Usage of the stack in reading:         Tactical Reading.   (line    6)
* version:                               GTP command reference.
                                                             (line   55)
* weakness:                              Dragons.            (line  199)
* worm <1>:                              Worms.              (line    6)
* worm:                                  Worms and Dragons.  (line   27)
* worm_cutstone:                         GTP command reference.
                                                             (line  847)
* worm_data:                             GTP command reference.
                                                             (line  806)
* worm_stones:                           GTP command reference.
                                                             (line  841)
* Zobrist hashing algorithm:             Hashing.            (line    6)