1 /* specfunc/bessel_temme.c
3 * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 3 of the License, or (at
8 * your option) any later version.
10 * This program is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
20 /* Author: G. Jungman */
22 /* Calculate series for Y_nu and K_nu for small x and nu.
23 * This is applicable for x < 2 and |nu|<=1/2.
24 * These functions assume x > 0.
27 #include <gsl/gsl_math.h>
28 #include <gsl/gsl_errno.h>
29 #include <gsl/gsl_mode.h>
30 #include "bessel_temme.h"
32 #include "chebyshev.h"
33 #include "cheb_eval.c"
35 /* nu = (x+1)/4, -1<x<1, 1/(2nu)(1/Gamma[1-nu]-1/Gamma[1+nu]) */
36 static double g1_dat[14] = {
37 -1.14516408366268311786898152867,
38 0.00636085311347084238122955495,
39 0.00186245193007206848934643657,
40 0.000152833085873453507081227824,
41 0.000017017464011802038795324732,
42 -6.4597502923347254354668326451e-07,
43 -5.1819848432519380894104312968e-08,
44 4.5189092894858183051123180797e-10,
45 3.2433227371020873043666259180e-11,
46 6.8309434024947522875432400828e-13,
47 2.8353502755172101513119628130e-14,
48 -7.9883905769323592875638087541e-16,
49 -3.3726677300771949833341213457e-17,
50 -3.6586334809210520744054437104e-20
52 static cheb_series g1_cs = {
59 /* nu = (x+1)/4, -1<x<1, 1/2 (1/Gamma[1-nu]+1/Gamma[1+nu]) */
60 static double g2_dat[15] =
62 1.882645524949671835019616975350,
63 -0.077490658396167518329547945212,
64 -0.018256714847324929419579340950,
65 0.0006338030209074895795923971731,
66 0.0000762290543508729021194461175,
67 -9.5501647561720443519853993526e-07,
68 -8.8927268107886351912431512955e-08,
69 -1.9521334772319613740511880132e-09,
70 -9.4003052735885162111769579771e-11,
71 4.6875133849532393179290879101e-12,
72 2.2658535746925759582447545145e-13,
73 -1.1725509698488015111878735251e-15,
74 -7.0441338200245222530843155877e-17,
75 -2.4377878310107693650659740228e-18,
76 -7.5225243218253901727164675011e-20
78 static cheb_series g2_cs = {
88 gsl_sf_temme_gamma(const double nu, double * g_1pnu, double * g_1mnu, double * g1, double * g2)
90 const double anu = fabs(nu); /* functions are even */
91 const double x = 4.0*anu - 1.0;
94 cheb_eval_e(&g1_cs, x, &r_g1);
95 cheb_eval_e(&g2_cs, x, &r_g2);
98 *g_1mnu = 1.0/(r_g2.val + nu * r_g1.val);
99 *g_1pnu = 1.0/(r_g2.val - nu * r_g1.val);
105 gsl_sf_bessel_Y_temme(const double nu, const double x,
107 gsl_sf_result * Ynup1)
109 const int max_iter = 15000;
111 const double half_x = 0.5 * x;
112 const double ln_half_x = log(half_x);
113 const double half_x_nu = exp(nu*ln_half_x);
114 const double pi_nu = M_PI * nu;
115 const double alpha = pi_nu / 2.0;
116 const double sigma = -nu * ln_half_x;
117 const double sinrat = (fabs(pi_nu) < GSL_DBL_EPSILON ? 1.0 : pi_nu/sin(pi_nu));
118 const double sinhrat = (fabs(sigma) < GSL_DBL_EPSILON ? 1.0 : sinh(sigma)/sigma);
119 const double sinhalf = (fabs(alpha) < GSL_DBL_EPSILON ? 1.0 : sin(alpha)/alpha);
120 const double sin_sqr = nu*M_PI*M_PI*0.5 * sinhalf*sinhalf;
123 double fk, pk, qk, hk, ck;
127 double g_1pnu, g_1mnu, g1, g2;
128 int stat_g = gsl_sf_temme_gamma(nu, &g_1pnu, &g_1mnu, &g1, &g2);
130 fk = 2.0/M_PI * sinrat * (cosh(sigma)*g1 - sinhrat*ln_half_x*g2);
131 pk = 1.0/M_PI /half_x_nu * g_1pnu;
132 qk = 1.0/M_PI *half_x_nu * g_1mnu;
136 sum0 = fk + sin_sqr * qk;
139 while(k < max_iter) {
144 fk = (k*fk + pk + qk)/(k*k-nu*nu);
145 ck *= -half_x*half_x/k;
148 gk = fk + sin_sqr * qk;
154 if(fabs(del0) < 0.5*(1.0 + fabs(sum0))*GSL_DBL_EPSILON) break;
158 Ynu->err = (2.0 + 0.5*k) * GSL_DBL_EPSILON * fabs(Ynu->val);
159 Ynup1->val = -sum1 * 2.0/x;
160 Ynup1->err = (2.0 + 0.5*k) * GSL_DBL_EPSILON * fabs(Ynup1->val);
162 stat_iter = ( k >= max_iter ? GSL_EMAXITER : GSL_SUCCESS );
163 return GSL_ERROR_SELECT_2(stat_iter, stat_g);
168 gsl_sf_bessel_K_scaled_temme(const double nu, const double x,
169 double * K_nu, double * K_nup1, double * Kp_nu)
171 const int max_iter = 15000;
173 const double half_x = 0.5 * x;
174 const double ln_half_x = log(half_x);
175 const double half_x_nu = exp(nu*ln_half_x);
176 const double pi_nu = M_PI * nu;
177 const double sigma = -nu * ln_half_x;
178 const double sinrat = (fabs(pi_nu) < GSL_DBL_EPSILON ? 1.0 : pi_nu/sin(pi_nu));
179 const double sinhrat = (fabs(sigma) < GSL_DBL_EPSILON ? 1.0 : sinh(sigma)/sigma);
180 const double ex = exp(x);
183 double fk, pk, qk, hk, ck;
187 double g_1pnu, g_1mnu, g1, g2;
188 int stat_g = gsl_sf_temme_gamma(nu, &g_1pnu, &g_1mnu, &g1, &g2);
190 fk = sinrat * (cosh(sigma)*g1 - sinhrat*ln_half_x*g2);
191 pk = 0.5/half_x_nu * g_1pnu;
192 qk = 0.5*half_x_nu * g_1mnu;
197 while(k < max_iter) {
201 fk = (k*fk + pk + qk)/(k*k-nu*nu);
202 ck *= half_x*half_x/k;
210 if(fabs(del0) < 0.5*fabs(sum0)*GSL_DBL_EPSILON) break;
214 *K_nup1 = sum1 * 2.0/x * ex;
215 *Kp_nu = - *K_nup1 + nu/x * *K_nu;
217 stat_iter = ( k == max_iter ? GSL_EMAXITER : GSL_SUCCESS );
218 return GSL_ERROR_SELECT_2(stat_iter, stat_g);