BSD 4_1c_2 release

[unix-history] / usr / src / usr.lib / libm / j0.c

/*      @(#)j0.c        4.1     12/25/82        */

/*
       floating point Bessel's function
       of the first and second kinds
       of order zero

       j0(x) returns the value of J0(x)
       for all real values of x.

       There are no error returns.
       Calls sin, cos, sqrt.

       There is a niggling bug in J0 which
       causes errors up to 2e-16 for x in the
       interval [-8,8].
       The bug is caused by an inappropriate order
       of summation of the series.  rhm will fix it
       someday.

       Coefficients are from Hart & Cheney.
       #5849 (19.22D)
       #6549 (19.25D)
       #6949 (19.41D)

       y0(x) returns the value of Y0(x)
       for positive real values of x.
       For x<=0, error number EDOM is set and a
       large negative value is returned.

       Calls sin, cos, sqrt, log, j0.

       The values of Y0 have not been checked
       to more than ten places.

       Coefficients are from Hart & Cheney.
       #6245 (18.78D)
       #6549 (19.25D)
       #6949 (19.41D)
*/

#include <math.h>
#include <errno.h>

int     errno;
static double pzero, qzero;
static double tpi       = .6366197723675813430755350535e0;
static double pio4      = .7853981633974483096156608458e0;
static double p1[] = {
       0.4933787251794133561816813446e21,
       -.1179157629107610536038440800e21,
       0.6382059341072356562289432465e19,
       -.1367620353088171386865416609e18,
       0.1434354939140344111664316553e16,
       -.8085222034853793871199468171e13,
       0.2507158285536881945555156435e11,
       -.4050412371833132706360663322e8,
       0.2685786856980014981415848441e5,
};
static double q1[] = {
       0.4933787251794133562113278438e21,
       0.5428918384092285160200195092e19,
       0.3024635616709462698627330784e17,
       0.1127756739679798507056031594e15,
       0.3123043114941213172572469442e12,
       0.6699987672982239671814028660e9,
       0.1114636098462985378182402543e7,
       0.1363063652328970604442810507e4,
       1.0
};
static double p2[] = {
       0.5393485083869438325262122897e7,
       0.1233238476817638145232406055e8,
       0.8413041456550439208464315611e7,
       0.2016135283049983642487182349e7,
       0.1539826532623911470917825993e6,
       0.2485271928957404011288128951e4,
       0.0,
};
static double q2[] = {
       0.5393485083869438325560444960e7,
       0.1233831022786324960844856182e8,
       0.8426449050629797331554404810e7,
       0.2025066801570134013891035236e7,
       0.1560017276940030940592769933e6,
       0.2615700736920839685159081813e4,
       1.0,
};
static double p3[] = {
       -.3984617357595222463506790588e4,
       -.1038141698748464093880530341e5,
       -.8239066313485606568803548860e4,
       -.2365956170779108192723612816e4,
       -.2262630641933704113967255053e3,
       -.4887199395841261531199129300e1,
       0.0,
};
static double q3[] = {
       0.2550155108860942382983170882e6,
       0.6667454239319826986004038103e6,
       0.5332913634216897168722255057e6,
       0.1560213206679291652539287109e6,
       0.1570489191515395519392882766e5,
       0.4087714673983499223402830260e3,
       1.0,
};
static double p4[] = {
       -.2750286678629109583701933175e20,
       0.6587473275719554925999402049e20,
       -.5247065581112764941297350814e19,
       0.1375624316399344078571335453e18,
       -.1648605817185729473122082537e16,
       0.1025520859686394284509167421e14,
       -.3436371222979040378171030138e11,
       0.5915213465686889654273830069e8,
       -.4137035497933148554125235152e5,
};
static double q4[] = {
       0.3726458838986165881989980e21,
       0.4192417043410839973904769661e19,
       0.2392883043499781857439356652e17,
       0.9162038034075185262489147968e14,
       0.2613065755041081249568482092e12,
       0.5795122640700729537480087915e9,
       0.1001702641288906265666651753e7,
       0.1282452772478993804176329391e4,
       1.0,
};

double
j0(arg) double arg;{
       double argsq, n, d;
       double sin(), cos(), sqrt();
       int i;

       if(arg < 0.) arg = -arg;
       if(arg > 8.){
               asympt(arg);
               n = arg - pio4;
               return(sqrt(tpi/arg)*(pzero*cos(n) - qzero*sin(n)));
       }
       argsq = arg*arg;
       for(n=0,d=0,i=8;i>=0;i--){
               n = n*argsq + p1[i];
               d = d*argsq + q1[i];
       }
       return(n/d);
}

double
y0(arg) double arg;{
       double argsq, n, d;
       double sin(), cos(), sqrt(), log(), j0();
       int i;

       errno = 0;
       if(arg <= 0.){
               errno = EDOM;
               return(-HUGE);
       }
       if(arg > 8.){
               asympt(arg);
               n = arg - pio4;
               return(sqrt(tpi/arg)*(pzero*sin(n) + qzero*cos(n)));
       }
       argsq = arg*arg;
       for(n=0,d=0,i=8;i>=0;i--){
               n = n*argsq + p4[i];
               d = d*argsq + q4[i];
       }
       return(n/d + tpi*j0(arg)*log(arg));
}

static
asympt(arg) double arg;{
       double zsq, n, d;
       int i;
       zsq = 64./(arg*arg);
       for(n=0,d=0,i=6;i>=0;i--){
               n = n*zsq + p2[i];
               d = d*zsq + q2[i];
       }
       pzero = n/d;
       for(n=0,d=0,i=6;i>=0;i--){
               n = n*zsq + p3[i];
               d = d*zsq + q3[i];
       }
       qzero = (8./arg)*(n/d);
}