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/* cheb/integ.c
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*
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* Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or (at
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* your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include <config.h>
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#include <stdlib.h>
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#include <gsl/gsl_math.h>
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#include <gsl/gsl_errno.h>
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#include <gsl/gsl_chebyshev.h>
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int gsl_cheb_calc_integ(gsl_cheb_series * integ, const gsl_cheb_series * f)
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{
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const size_t n = f->order + 1;
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const double con = 0.25 * (f->b - f->a);
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if(integ->order != f->order)
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{
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GSL_ERROR ("order of chebyshev series must be equal", GSL_ENOMEM);
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}
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/* set the other parameters in the chebyshev struct */
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integ->a = f->a;
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integ->b = f->b;
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/* FIXME: should probably set integ->f[] as well */
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if(n == 1) {
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integ->c[0] = 0.;
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}
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else if(n == 2) {
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integ->c[1] = con * f->c[0];
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integ->c[0] = 2.0 * integ->c[1];
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}
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else {
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double sum = 0.0;
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double fac = 1.0;
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size_t i;
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for(i=1; i<=n-2; i++) {
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integ->c[i] = con * (f->c[i-1] - f->c[i+1])/((double)i);
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sum += fac * integ->c[i];
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fac = -fac;
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}
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integ->c[n-1] = con * f->c[n-2]/(n-1.0);
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sum += fac * integ->c[n-1];
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integ->c[0] = 2.0 * sum;
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}
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return GSL_SUCCESS;
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}
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