/* multimin/diff.c *  * Copyright (C) 2000 David Morrison *  * 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., 675 Mass Ave, Cambridge, MA 02139, USA. */#include <config.h>#include <gsl/gsl_multimin.h>intgsl_multimin_diff (const gsl_multimin_function * f,                   const gsl_vector * x, gsl_vector * g){  size_t i, n = f->n;  double h = GSL_SQRT_DBL_EPSILON;  gsl_vector * x1 = gsl_vector_alloc (n);  /* FIXME: pass as argument */  gsl_vector_memcpy (x1, x);  for (i = 0; i < n; i++)    {      double fl, fh;        double xi = gsl_vector_get (x, i);      double dx = fabs(xi) * h;      if (dx == 0.0) dx = h;      gsl_vector_set (x1, i, xi + dx);      fh = GSL_MULTIMIN_FN_EVAL(f, x1);      gsl_vector_set (x1, i, xi - dx);      fl = GSL_MULTIMIN_FN_EVAL(f, x1);      gsl_vector_set (x1, i, xi);      gsl_vector_set (g, i, (fh - fl) / (2.0 * dx));    }  gsl_vector_free (x1);  return GSL_SUCCESS;}