| /* cheb/deriv.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_deriv(gsl_cheb_series * deriv, const gsl_cheb_series * f) |
| { |
| const size_t n = f->order + 1; |
| const double con = 2.0 / (f->b - f->a); |
| size_t i; |
| |
| if(deriv->order != f->order) |
| { |
| GSL_ERROR ("order of chebyshev series must be equal", GSL_ENOMEM); |
| } |
| |
| /* set the other parameters in the chebyshev struct */ |
| |
| deriv->a = f->a; |
| deriv->b = f->b; |
| |
| #ifdef ERR |
| deriv->err = n * n * f->c[n-1]; /* error in derivative is n^2 c_n */ |
| #endif |
| |
| /* FIXME: should probably set deriv->f[] as well */ |
| |
| deriv->c[n-1] = 0.0; |
| |
| if(n > 1) { |
| deriv->c[n-2] = 2.0 *(n-1.0) * f->c[n-1]; |
| |
| for(i = n-3; i>0; i--) |
| deriv->c[i] = deriv->c[i+2] + 2.0 *(i+1.0) * f->c[i+1]; |
| |
| deriv->c[0] = deriv->c[2] + 2.0 * f->c[1]; |
| |
| for(i = 0 ; i<n ; i++) |
| deriv->c[i] *= con; |
| } |
| |
| return GSL_SUCCESS; |
| } |