| /* cheb/integ.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 2 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. |
| */ |
| |
| #include <config.h> |
| #include <stdlib.h> |
| #include <gsl/gsl_math.h> |
| #include <gsl/gsl_errno.h> |
| #include <gsl/gsl_chebyshev.h> |
| |
| int gsl_cheb_calc_integ(gsl_cheb_series * integ, const gsl_cheb_series * f) |
| { |
| const size_t n = f->order + 1; |
| const double con = 0.25 * (f->b - f->a); |
| |
| if(integ->order != f->order) |
| { |
| GSL_ERROR ("order of chebyshev series must be equal", GSL_ENOMEM); |
| } |
| |
| /* set the other parameters in the chebyshev struct */ |
| |
| integ->a = f->a; |
| integ->b = f->b; |
| |
| /* FIXME: should probably set integ->f[] as well */ |
| |
| if(n == 1) { |
| integ->c[0] = 0.; |
| } |
| else if(n == 2) { |
| integ->c[1] = con * f->c[0]; |
| integ->c[0] = 2.0 * integ->c[1]; |
| } |
| else { |
| double sum = 0.0; |
| double fac = 1.0; |
| size_t i; |
| for(i=1; i<=n-2; i++) { |
| integ->c[i] = con * (f->c[i-1] - f->c[i+1])/((double)i); |
| sum += fac * integ->c[i]; |
| fac = -fac; |
| } |
| integ->c[n-1] = con * f->c[n-2]/(n-1.0); |
| sum += fac * integ->c[n-1]; |
| integ->c[0] = 2.0 * sum; |
| } |
| |
| return GSL_SUCCESS; |
| } |