1 files changed, 100 insertions, 0 deletions
diff --git a/gsl-1.9/randist/binomial.c b/gsl-1.9/randist/binomial.c
new file mode 100644
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+++ b/gsl-1.9/randist/binomial.c
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+/* randist/binomial.c
+ * 
+ * Copyright (C) 1996, 1997, 1998, 1999, 2000 James Theiler, 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_sys.h>
+#include <gsl/gsl_rng.h>
+#include <gsl/gsl_randist.h>
+#include <gsl/gsl_sf_gamma.h>
+
+/* The binomial distribution has the form,
+
+   prob(k) =  n!/(k!(n-k)!) *  p^k (1-p)^(n-k) for k = 0, 1, ..., n
+
+   This is the algorithm from Knuth */
+
+/* Default binomial generator is now in binomial_tpe.c */
+
+unsigned int
+gsl_ran_binomial_knuth (const gsl_rng * r, double p, unsigned int n)
+{
+  unsigned int i, a, b, k = 0;
+
+  while (n > 10)        /* This parameter is tunable */
+    {
+      double X;
+      a = 1 + (n / 2);
+      b = 1 + n - a;
+
+      X = gsl_ran_beta (r, (double) a, (double) b);
+
+      if (X >= p)
+        {
+          n = a - 1;
+          p /= X;
+        }
+      else
+        {
+          k += a;
+          n = b - 1;
+          p = (p - X) / (1 - X);
+        }
+    }
+
+  for (i = 0; i < n; i++)
+    {
+      double u = gsl_rng_uniform (r);
+      if (u < p)
+        k++;
+    }
+
+  return k;
+}
+
+double
+gsl_ran_binomial_pdf (const unsigned int k, const double p,
+                      const unsigned int n)
+{
+  if (k > n)
+    {
+      return 0;
+    }
+  else
+    {
+      double P;
+
+      if (p == 0) 
+        {
+          P = (k == 0) ? 1 : 0;
+        }
+      else if (p == 1)
+        {
+          P = (k == n) ? 1 : 0;
+        }
+      else
+        {
+          double ln_Cnk = gsl_sf_lnchoose (n, k);
+          P = ln_Cnk + k * log (p) + (n - k) * log1p (-p);
+          P = exp (P);
+        }
+
+      return P;
+    }
+}