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- /* specfunc/hyperg.c
- *
- * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
- *
- * 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, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
- */
- /* Author: G. Jungman */
- /* Miscellaneous implementations of use
- * for evaluation of hypergeometric functions.
- */
- #include "gsl__config.h"
- #include "gsl_math.h"
- #include "gsl_errno.h"
- #include "gsl_sf_exp.h"
- #include "gsl_sf_gamma.h"
- #include "gsl_specfunc__error.h"
- #include "gsl_specfunc__hyperg.h"
- #define SUM_LARGE (1.0e-5*GSL_DBL_MAX)
- int
- gsl_sf_hyperg_1F1_series_e(const double a, const double b, const double x,
- gsl_sf_result * result
- )
- {
- double an = a;
- double bn = b;
- double n = 1.0;
- double del = 1.0;
- double abs_del = 1.0;
- double max_abs_del = 1.0;
- double sum_val = 1.0;
- double sum_err = 0.0;
- while(abs_del/fabs(sum_val) > 0.25*GSL_DBL_EPSILON) {
- double u, abs_u;
- if(bn == 0.0) {
- DOMAIN_ERROR(result);
- }
- if(an == 0.0) {
- result->val = sum_val;
- result->err = sum_err;
- result->err += 2.0 * GSL_DBL_EPSILON * n * fabs(sum_val);
- return GSL_SUCCESS;
- }
- if (n > 10000.0) {
- result->val = sum_val;
- result->err = sum_err;
- GSL_ERROR ("hypergeometric series failed to converge", GSL_EFAILED);
- }
- u = x * (an/(bn*n));
- abs_u = fabs(u);
- if(abs_u > 1.0 && max_abs_del > GSL_DBL_MAX/abs_u) {
- result->val = sum_val;
- result->err = fabs(sum_val);
- GSL_ERROR ("overflow", GSL_EOVRFLW);
- }
- del *= u;
- sum_val += del;
- if(fabs(sum_val) > SUM_LARGE) {
- result->val = sum_val;
- result->err = fabs(sum_val);
- GSL_ERROR ("overflow", GSL_EOVRFLW);
- }
- abs_del = fabs(del);
- max_abs_del = GSL_MAX_DBL(abs_del, max_abs_del);
- sum_err += 2.0*GSL_DBL_EPSILON*abs_del;
- an += 1.0;
- bn += 1.0;
- n += 1.0;
- }
- result->val = sum_val;
- result->err = sum_err;
- result->err += abs_del;
- result->err += 2.0 * GSL_DBL_EPSILON * n * fabs(sum_val);
- return GSL_SUCCESS;
- }
- int
- gsl_sf_hyperg_1F1_large_b_e(const double a, const double b, const double x, gsl_sf_result * result)
- {
- if(fabs(x/b) < 1.0) {
- const double u = x/b;
- const double v = 1.0/(1.0-u);
- const double pre = pow(v,a);
- const double uv = u*v;
- const double uv2 = uv*uv;
- const double t1 = a*(a+1.0)/(2.0*b)*uv2;
- const double t2a = a*(a+1.0)/(24.0*b*b)*uv2;
- const double t2b = 12.0 + 16.0*(a+2.0)*uv + 3.0*(a+2.0)*(a+3.0)*uv2;
- const double t2 = t2a*t2b;
- result->val = pre * (1.0 - t1 + t2);
- result->err = pre * GSL_DBL_EPSILON * (1.0 + fabs(t1) + fabs(t2));
- result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val);
- return GSL_SUCCESS;
- }
- else {
- DOMAIN_ERROR(result);
- }
- }
- int
- gsl_sf_hyperg_U_large_b_e(const double a, const double b, const double x,
- gsl_sf_result * result,
- double * ln_multiplier
- )
- {
- double N = floor(b); /* b = N + eps */
- double eps = b - N;
-
- if(fabs(eps) < GSL_SQRT_DBL_EPSILON) {
- double lnpre_val;
- double lnpre_err;
- gsl_sf_result M;
- if(b > 1.0) {
- double tmp = (1.0-b)*log(x);
- gsl_sf_result lg_bm1;
- gsl_sf_result lg_a;
- gsl_sf_lngamma_e(b-1.0, &lg_bm1);
- gsl_sf_lngamma_e(a, &lg_a);
- lnpre_val = tmp + x + lg_bm1.val - lg_a.val;
- lnpre_err = lg_bm1.err + lg_a.err + GSL_DBL_EPSILON * (fabs(x) + fabs(tmp));
- gsl_sf_hyperg_1F1_large_b_e(1.0-a, 2.0-b, -x, &M);
- }
- else {
- gsl_sf_result lg_1mb;
- gsl_sf_result lg_1pamb;
- gsl_sf_lngamma_e(1.0-b, &lg_1mb);
- gsl_sf_lngamma_e(1.0+a-b, &lg_1pamb);
- lnpre_val = lg_1mb.val - lg_1pamb.val;
- lnpre_err = lg_1mb.err + lg_1pamb.err;
- gsl_sf_hyperg_1F1_large_b_e(a, b, x, &M);
- }
- if(lnpre_val > GSL_LOG_DBL_MAX-10.0) {
- result->val = M.val;
- result->err = M.err;
- *ln_multiplier = lnpre_val;
- GSL_ERROR ("overflow", GSL_EOVRFLW);
- }
- else {
- gsl_sf_result epre;
- int stat_e = gsl_sf_exp_err_e(lnpre_val, lnpre_err, &epre);
- result->val = epre.val * M.val;
- result->err = epre.val * M.err + epre.err * fabs(M.val);
- result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val);
- *ln_multiplier = 0.0;
- return stat_e;
- }
- }
- else {
- double omb_lnx = (1.0-b)*log(x);
- gsl_sf_result lg_1mb; double sgn_1mb;
- gsl_sf_result lg_1pamb; double sgn_1pamb;
- gsl_sf_result lg_bm1; double sgn_bm1;
- gsl_sf_result lg_a; double sgn_a;
- gsl_sf_result M1, M2;
- double lnpre1_val, lnpre2_val;
- double lnpre1_err, lnpre2_err;
- double sgpre1, sgpre2;
- gsl_sf_hyperg_1F1_large_b_e( a, b, x, &M1);
- gsl_sf_hyperg_1F1_large_b_e(1.0-a, 2.0-b, x, &M2);
- gsl_sf_lngamma_sgn_e(1.0-b, &lg_1mb, &sgn_1mb);
- gsl_sf_lngamma_sgn_e(1.0+a-b, &lg_1pamb, &sgn_1pamb);
- gsl_sf_lngamma_sgn_e(b-1.0, &lg_bm1, &sgn_bm1);
- gsl_sf_lngamma_sgn_e(a, &lg_a, &sgn_a);
- lnpre1_val = lg_1mb.val - lg_1pamb.val;
- lnpre1_err = lg_1mb.err + lg_1pamb.err;
- lnpre2_val = lg_bm1.val - lg_a.val - omb_lnx - x;
- lnpre2_err = lg_bm1.err + lg_a.err + GSL_DBL_EPSILON * (fabs(omb_lnx)+fabs(x));
- sgpre1 = sgn_1mb * sgn_1pamb;
- sgpre2 = sgn_bm1 * sgn_a;
- if(lnpre1_val > GSL_LOG_DBL_MAX-10.0 || lnpre2_val > GSL_LOG_DBL_MAX-10.0) {
- double max_lnpre_val = GSL_MAX(lnpre1_val,lnpre2_val);
- double max_lnpre_err = GSL_MAX(lnpre1_err,lnpre2_err);
- double lp1 = lnpre1_val - max_lnpre_val;
- double lp2 = lnpre2_val - max_lnpre_val;
- double t1 = sgpre1*exp(lp1);
- double t2 = sgpre2*exp(lp2);
- result->val = t1*M1.val + t2*M2.val;
- result->err = fabs(t1)*M1.err + fabs(t2)*M2.err;
- result->err += GSL_DBL_EPSILON * exp(max_lnpre_err) * (fabs(t1*M1.val) + fabs(t2*M2.val));
- result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val);
- *ln_multiplier = max_lnpre_val;
- GSL_ERROR ("overflow", GSL_EOVRFLW);
- }
- else {
- double t1 = sgpre1*exp(lnpre1_val);
- double t2 = sgpre2*exp(lnpre2_val);
- result->val = t1*M1.val + t2*M2.val;
- result->err = fabs(t1) * M1.err + fabs(t2)*M2.err;
- result->err += GSL_DBL_EPSILON * (exp(lnpre1_err)*fabs(t1*M1.val) + exp(lnpre2_err)*fabs(t2*M2.val));
- result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val);
- *ln_multiplier = 0.0;
- return GSL_SUCCESS;
- }
- }
- }
- /* [Carlson, p.109] says the error in truncating this asymptotic series
- * is less than the absolute value of the first neglected term.
- *
- * A termination argument is provided, so that the series will
- * be summed at most up to n=n_trunc. If n_trunc is set negative,
- * then the series is summed until it appears to start diverging.
- */
- int
- gsl_sf_hyperg_2F0_series_e(const double a, const double b, const double x,
- int n_trunc,
- gsl_sf_result * result
- )
- {
- const int maxiter = 2000;
- double an = a;
- double bn = b;
- double n = 1.0;
- double sum = 1.0;
- double del = 1.0;
- double abs_del = 1.0;
- double max_abs_del = 1.0;
- double last_abs_del = 1.0;
-
- while(abs_del/fabs(sum) > GSL_DBL_EPSILON && n < maxiter) {
- double u = an * (bn/n * x);
- double abs_u = fabs(u);
- if(abs_u > 1.0 && (max_abs_del > GSL_DBL_MAX/abs_u)) {
- result->val = sum;
- result->err = fabs(sum);
- GSL_ERROR ("overflow", GSL_EOVRFLW);
- }
- del *= u;
- sum += del;
- abs_del = fabs(del);
- if(abs_del > last_abs_del) break; /* series is probably starting to grow */
- last_abs_del = abs_del;
- max_abs_del = GSL_MAX(abs_del, max_abs_del);
- an += 1.0;
- bn += 1.0;
- n += 1.0;
-
- if(an == 0.0 || bn == 0.0) break; /* series terminated */
-
- if(n_trunc >= 0 && n >= n_trunc) break; /* reached requested timeout */
- }
- result->val = sum;
- result->err = GSL_DBL_EPSILON * n + abs_del;
- if(n >= maxiter)
- GSL_ERROR ("error", GSL_EMAXITER);
- else
- return GSL_SUCCESS;
- }
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