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diff --git a/gsl-1.9/cdf/logistic.c b/gsl-1.9/cdf/logistic.c
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+/* cdf/logistic.c
+ *
+ * Copyright (C) 2003 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>
+#include <gsl/gsl_cdf.h>
+
+double
+gsl_cdf_logistic_P (const double x, const double a)
+{
+ double P;
+ double u = x / a;
+
+ if (u >= 0)
+ {
+ P = 1 / (1 + exp (-u));
+ }
+ else
+ {
+ P = exp (u) / (1 + exp (u));
+ }
+
+ return P;
+}
+
+double
+gsl_cdf_logistic_Q (const double x, const double a)
+{
+ double Q;
+ double u = x / a;
+
+ if (u >= 0)
+ {
+ Q = exp (-u) / (1 + exp (-u));
+ }
+ else
+ {
+ Q = 1 / (1 + exp (u));
+ }
+
+ return Q;
+}