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/* sys/expm1.c
*
* Copyright (C) 1996, 1997, 1998, 1999, 2000 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 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 <math.h>
#include <gsl/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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