+/*
+ floating point Bessel's function
+ of the first and second kinds
+ of order one
+
+ j1(x) returns the value of J1(x)
+ for all real values of x.
+
+ There are no error returns.
+ Calls sin, cos, sqrt.
+
+ There is a niggling bug in J1 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.
+ #6050 (20.98D)
+ #6750 (19.19D)
+ #7150 (19.35D)
+
+ y1(x) returns the value of Y1(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, j1.
+
+ The values of Y1 have not been checked
+ to more than ten places.
+
+ Coefficients are from Hart & Cheney.
+ #6447 (22.18D)
+ #6750 (19.19D)
+ #7150 (19.35D)
+*/
+
+#include <math.h>
+#include <errno.h>
+
+int errno;
+static double pzero, qzero;
+static double tpi = .6366197723675813430755350535e0;
+static double pio4 = .7853981633974483096156608458e0;
+static double p1[] = {
+ 0.581199354001606143928050809e21,
+ -.6672106568924916298020941484e20,
+ 0.2316433580634002297931815435e19,
+ -.3588817569910106050743641413e17,
+ 0.2908795263834775409737601689e15,
+ -.1322983480332126453125473247e13,
+ 0.3413234182301700539091292655e10,
+ -.4695753530642995859767162166e7,
+ 0.2701122710892323414856790990e4,
+};
+static double q1[] = {
+ 0.1162398708003212287858529400e22,
+ 0.1185770712190320999837113348e20,
+ 0.6092061398917521746105196863e17,
+ 0.2081661221307607351240184229e15,
+ 0.5243710262167649715406728642e12,
+ 0.1013863514358673989967045588e10,
+ 0.1501793594998585505921097578e7,
+ 0.1606931573481487801970916749e4,
+ 1.0,
+};
+static double p2[] = {
+ -.4435757816794127857114720794e7,
+ -.9942246505077641195658377899e7,
+ -.6603373248364939109255245434e7,
+ -.1523529351181137383255105722e7,
+ -.1098240554345934672737413139e6,
+ -.1611616644324610116477412898e4,
+ 0.0,
+};
+static double q2[] = {
+ -.4435757816794127856828016962e7,
+ -.9934124389934585658967556309e7,
+ -.6585339479723087072826915069e7,
+ -.1511809506634160881644546358e7,
+ -.1072638599110382011903063867e6,
+ -.1455009440190496182453565068e4,
+ 1.0,
+};
+static double p3[] = {
+ 0.3322091340985722351859704442e5,
+ 0.8514516067533570196555001171e5,
+ 0.6617883658127083517939992166e5,
+ 0.1849426287322386679652009819e5,
+ 0.1706375429020768002061283546e4,
+ 0.3526513384663603218592175580e2,
+ 0.0,
+};
+static double q3[] = {
+ 0.7087128194102874357377502472e6,
+ 0.1819458042243997298924553839e7,
+ 0.1419460669603720892855755253e7,
+ 0.4002944358226697511708610813e6,
+ 0.3789022974577220264142952256e5,
+ 0.8638367769604990967475517183e3,
+ 1.0,
+};
+static double p4[] = {
+ -.9963753424306922225996744354e23,
+ 0.2655473831434854326894248968e23,
+ -.1212297555414509577913561535e22,
+ 0.2193107339917797592111427556e20,
+ -.1965887462722140658820322248e18,
+ 0.9569930239921683481121552788e15,
+ -.2580681702194450950541426399e13,
+ 0.3639488548124002058278999428e10,
+ -.2108847540133123652824139923e7,
+ 0.0,
+};
+static double q4[] = {
+ 0.5082067366941243245314424152e24,
+ 0.5435310377188854170800653097e22,
+ 0.2954987935897148674290758119e20,
+ 0.1082258259408819552553850180e18,
+ 0.2976632125647276729292742282e15,
+ 0.6465340881265275571961681500e12,
+ 0.1128686837169442121732366891e10,
+ 0.1563282754899580604737366452e7,
+ 0.1612361029677000859332072312e4,
+ 1.0,
+};
+
+double
+j1(arg) double arg;{
+ double xsq, n, d, x;
+ double sin(), cos(), sqrt();
+ int i;
+
+ x = arg;
+ if(x < 0.) x = -x;
+ if(x > 8.){
+ asympt(x);
+ n = x - 3.*pio4;
+ n = sqrt(tpi/x)*(pzero*cos(n) - qzero*sin(n));
+ if(arg <0.) n = -n;
+ return(n);
+ }
+ xsq = x*x;
+ for(n=0,d=0,i=8;i>=0;i--){
+ n = n*xsq + p1[i];
+ d = d*xsq + q1[i];
+ }
+ return(arg*n/d);
+}
+
+double
+y1(arg) double arg;{
+ double xsq, n, d, x;
+ double sin(), cos(), sqrt(), log(), j1();
+ int i;
+
+ errno = 0;
+ x = arg;
+ if(x <= 0.){
+ errno = EDOM;
+ return(-HUGE);
+ }
+ if(x > 8.){
+ asympt(x);
+ n = x - 3*pio4;
+ return(sqrt(tpi/x)*(pzero*sin(n) + qzero*cos(n)));
+ }
+ xsq = x*x;
+ for(n=0,d=0,i=9;i>=0;i--){
+ n = n*xsq + p4[i];
+ d = d*xsq + q4[i];
+ }
+ return(x*n/d + tpi*(j1(x)*log(x)-1./x));
+}
+
+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);
+}