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- /* specfunc/bessel_Knu.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 */
- #include "gsl__config.h"
- #include "gsl_math.h"
- #include "gsl_errno.h"
- #include "gsl_sf_exp.h"
- #include "gsl_sf_gamma.h"
- #include "gsl_sf_bessel.h"
- #include "gsl_specfunc__error.h"
- #include "gsl_specfunc__bessel.h"
- #include "gsl_specfunc__bessel_temme.h"
- /*-*-*-*-*-*-*-*-*-*-*-* Functions with Error Codes *-*-*-*-*-*-*-*-*-*-*-*/
- int
- gsl_sf_bessel_Knu_scaled_e(const double nu, const double x, gsl_sf_result * result)
- {
- /* CHECK_POINTER(result) */
- if(x <= 0.0 || nu < 0.0) {
- DOMAIN_ERROR(result);
- }
- else {
- int N = (int)(nu + 0.5);
- double mu = nu - N; /* -1/2 <= mu <= 1/2 */
- double K_mu, K_mup1, Kp_mu;
- double K_nu, K_nup1, K_num1;
- int n;
- if(x < 2.0) {
- gsl_sf_bessel_K_scaled_temme(mu, x, &K_mu, &K_mup1, &Kp_mu);
- }
- else {
- gsl_sf_bessel_K_scaled_steed_temme_CF2(mu, x, &K_mu, &K_mup1, &Kp_mu);
- }
- /* recurse forward to obtain K_num1, K_nu */
- K_nu = K_mu;
- K_nup1 = K_mup1;
- for(n=0; n<N; n++) {
- K_num1 = K_nu;
- K_nu = K_nup1;
- K_nup1 = 2.0*(mu+n+1)/x * K_nu + K_num1;
- }
- result->val = K_nu;
- result->err = 2.0 * GSL_DBL_EPSILON * (N + 4.0) * fabs(result->val);
- return GSL_SUCCESS;
- }
- }
- int
- gsl_sf_bessel_Knu_e(const double nu, const double x, gsl_sf_result * result)
- {
- gsl_sf_result b;
- int stat_K = gsl_sf_bessel_Knu_scaled_e(nu, x, &b);
- int stat_e = gsl_sf_exp_mult_err_e(-x, 0.0, b.val, b.err, result);
- return GSL_ERROR_SELECT_2(stat_e, stat_K);
- }
- int
- gsl_sf_bessel_lnKnu_e(const double nu, const double x, gsl_sf_result * result)
- {
- /* CHECK_POINTER(result) */
- if(x <= 0.0 || nu < 0.0) {
- DOMAIN_ERROR(result);
- }
- else if(nu == 0.0) {
- gsl_sf_result K_scaled;
- /* This cannot underflow, and
- * it will not throw GSL_EDOM
- * since that is already checked.
- */
- gsl_sf_bessel_K0_scaled_e(x, &K_scaled);
- result->val = -x + log(fabs(K_scaled.val));
- result->err = GSL_DBL_EPSILON * fabs(x) + fabs(K_scaled.err/K_scaled.val);
- result->err += GSL_DBL_EPSILON * fabs(result->val);
- return GSL_SUCCESS;
- }
- else if(x < 2.0 && nu > 1.0) {
- /* Make use of the inequality
- * Knu(x) <= 1/2 (2/x)^nu Gamma(nu),
- * which follows from the integral representation
- * [Abramowitz+Stegun, 9.6.23 (2)]. With this
- * we decide whether or not there is an overflow
- * problem because x is small.
- */
- double ln_bound;
- gsl_sf_result lg_nu;
- gsl_sf_lngamma_e(nu, &lg_nu);
- ln_bound = -M_LN2 - nu*log(0.5*x) + lg_nu.val;
- if(ln_bound > GSL_LOG_DBL_MAX - 20.0) {
- /* x must be very small or nu very large (or both).
- */
- double xi = 0.25*x*x;
- double sum = 1.0 - xi/(nu-1.0);
- if(nu > 2.0) sum += (xi/(nu-1.0)) * (xi/(nu-2.0));
- result->val = ln_bound + log(sum);
- result->err = lg_nu.err;
- result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val);
- return GSL_SUCCESS;
- }
- /* can drop-through here */
- }
- {
- /* We passed the above tests, so no problem.
- * Evaluate as usual. Note the possible drop-through
- * in the above code!
- */
- gsl_sf_result K_scaled;
- gsl_sf_bessel_Knu_scaled_e(nu, x, &K_scaled);
- result->val = -x + log(fabs(K_scaled.val));
- result->err = GSL_DBL_EPSILON * fabs(x) + fabs(K_scaled.err/K_scaled.val);
- result->err += GSL_DBL_EPSILON * fabs(result->val);
- return GSL_SUCCESS;
- }
- }
- /*-*-*-*-*-*-*-*-*-* Functions w/ Natural Prototypes *-*-*-*-*-*-*-*-*-*-*/
- #include "gsl_specfunc__eval.h"
- double gsl_sf_bessel_Knu_scaled(const double nu, const double x)
- {
- EVAL_RESULT(gsl_sf_bessel_Knu_scaled_e(nu, x, &result));
- }
- double gsl_sf_bessel_Knu(const double nu, const double x)
- {
- EVAL_RESULT(gsl_sf_bessel_Knu_e(nu, x, &result));
- }
- double gsl_sf_bessel_lnKnu(const double nu, const double x)
- {
- EVAL_RESULT(gsl_sf_bessel_lnKnu_e(nu, x, &result));
- }
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