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- /* sys/expm1.c
- *
- * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Gerard Jungman, Brian Gough
- *
- * 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 3 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 "gsl__config.h"
- #include <math.h>
- #include "gsl_math.h"
- double gsl_expm1 (const double x)
- {
- /* FIXME: this should be improved */
- if (fabs(x) < M_LN2)
- {
- /* Compute the taylor series S = x + (1/2!) x^2 + (1/3!) x^3 + ... */
- double i = 1.0;
- double sum = x;
- double term = x / 1.0;
- do
- {
- i++ ;
- term *= x/i;
- sum += term;
- }
- while (fabs(term) > fabs(sum) * GSL_DBL_EPSILON) ;
-
- return sum ;
- }
- else
- {
- return exp(x) - 1;
- }
- }
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