1 files changed, 124 insertions, 0 deletions
diff --git a/gsl-1.9/randist/hyperg.c b/gsl-1.9/randist/hyperg.c
new file mode 100644
index 0000000..c15de09
--- /dev/null
+++ b/gsl-1.9/randist/hyperg.c
@@ -0,0 +1,124 @@
+/* randist/hyperg.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_rng.h>
+#include <gsl/gsl_randist.h>
+#include <gsl/gsl_sf_gamma.h>
+
+/* The hypergeometric distribution has the form,
+
+   prob(k) =  choose(n1,t) choose(n2, t-k) / choose(n1+n2,t)
+
+   where choose(a,b) = a!/(b!(a-b)!) 
+
+   n1 + n2 is the total population (tagged plus untagged)
+   n1 is the tagged population
+   t is the number of samples taken (without replacement)
+   k is the number of tagged samples found
+
+*/
+
+unsigned int
+gsl_ran_hypergeometric (const gsl_rng * r, unsigned int n1, unsigned int n2, 
+                        unsigned int t)
+{
+  const unsigned int n = n1 + n2;
+
+  unsigned int i = 0;
+  unsigned int a = n1;
+  unsigned int b = n1 + n2;
+  unsigned int k = 0;
+
+  if (t > n)
+    {
+      t = n ;
+    }
+
+  if (t < n / 2) 
+    {
+      for (i = 0 ; i < t ; i++)
+        {
+          double u = gsl_rng_uniform(r) ;
+          
+          if (b * u < a)
+            {
+              k++ ;
+              if (k == n1)
+                return k ;
+              a-- ;
+            }
+          b-- ;
+        }
+      return k;
+    }
+  else
+    {
+      for (i = 0 ; i < n - t ; i++)
+        {
+          double u = gsl_rng_uniform(r) ;
+          
+          if (b * u < a)
+            {
+              k++ ;
+              if (k == n1)
+                return n1 - k ;
+              a-- ;
+            }
+          b-- ;
+        }
+      return n1 - k;
+    }
+
+
+}
+
+double
+gsl_ran_hypergeometric_pdf (const unsigned int k, 
+                            const unsigned int n1, 
+                            const unsigned int n2, 
+                            unsigned int t)
+{
+  if (t > n1 + n2)
+    {
+      t = n1 + n2 ;
+    }
+
+  if (k > n1 || k > t)
+    {
+      return 0 ;
+    }
+  else if (t > n2 && k + n2 < t )
+    {
+      return 0 ;
+    }
+  else 
+    {
+      double p;
+      
+      double c1 = gsl_sf_lnchoose(n1,k);
+      double c2 = gsl_sf_lnchoose(n2,t-k);
+      double c3 = gsl_sf_lnchoose(n1+n2,t);
+
+      p = exp(c1 + c2 - c3) ;
+
+      return p;
+    }
+}