| /* interpolation/interp_poly.c |
| * |
| * Copyright (C) 2001 DAN, HO-JIN |
| * |
| * 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. |
| */ |
| |
| /* Modified for standalone use in polynomial directory, B.Gough 2001 */ |
| |
| #include <config.h> |
| #include <gsl/gsl_errno.h> |
| #include <gsl/gsl_poly.h> |
| |
| int |
| gsl_poly_dd_init (double dd[], const double xa[], const double ya[], |
| size_t size) |
| { |
| size_t i, j; |
| |
| /* Newton's divided differences */ |
| |
| dd[0] = ya[0]; |
| |
| for (j = size - 1; j >= 1; j--) |
| { |
| dd[j] = (ya[j] - ya[j - 1]) / (xa[j] - xa[j - 1]); |
| } |
| |
| for (i = 2; i < size; i++) |
| { |
| for (j = size - 1; j >= i; j--) |
| { |
| dd[j] = (dd[j] - dd[j - 1]) / (xa[j] - xa[j - i]); |
| } |
| } |
| |
| return GSL_SUCCESS; |
| } |
| |
| #ifndef HIDE_INLINE_STATIC |
| double |
| gsl_poly_dd_eval (const double dd[], const double xa[], const size_t size, const double x) |
| { |
| size_t i; |
| double y = dd[size - 1]; |
| |
| for (i = size - 1; i--;) |
| { |
| y = dd[i] + (x - xa[i]) * y; |
| } |
| |
| return y; |
| } |
| #endif |
| |
| int |
| gsl_poly_dd_taylor (double c[], double xp, |
| const double dd[], const double xa[], size_t size, |
| double w[]) |
| { |
| size_t i, j; |
| |
| for (i = 0; i < size; i++) |
| { |
| c[i] = 0.0; |
| w[i] = 0.0; |
| } |
| |
| w[size - 1] = 1.0; |
| |
| c[0] = dd[0]; |
| |
| for (i = size - 1; i > 0 && i--;) |
| { |
| w[i] = -w[i + 1] * (xa[size - 2 - i] - xp); |
| |
| for (j = i + 1; j < size - 1; j++) |
| { |
| w[j] = w[j] - w[j + 1] * (xa[size - 2 - i] - xp); |
| } |
| |
| for (j = i; j < size; j++) |
| { |
| c[j - i] += w[j] * dd[size - i - 1]; |
| } |
| } |
| |
| return GSL_SUCCESS; |
| } |