1 files changed, 50 insertions, 0 deletions
diff --git a/gsl-1.9/sys/expm1.c b/gsl-1.9/sys/expm1.c
new file mode 100644
index 0000000..c79d063
--- /dev/null
+++ b/gsl-1.9/sys/expm1.c
@@ -0,0 +1,50 @@
+/* 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;
+    }
+}