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/* 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;
}
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