Changes in lemon/random.h [62:4790635473ef:92:5d4decd1b870] in lemon

File:

• lemon/random.h (modified) (3 diffs)

lemon/random.h

@@ -68 +68 @@
 
 #include <ctime>
-#include <cmath>
-
+
+#include <lemon/math.h>
 #include <lemon/dim2.h>
+
 ///\ingroup misc
 ///\file
@@ -760 +761 @@
       double xi,nu;
       const double delta = k-std::floor(k);
-      const double v0=M_E/(M_E-delta);
+      const double v0=E/(E-delta);
       do {
         double V0=1.0-real<double>();
@@ -803 +804 @@
     }  
       
+    /// Poisson distribution
+
+    /// This function generates a Poisson distribution random number with
+    /// parameter \c lambda.
+    /// 
+    /// The probability mass function of this distribusion is
+    /// \f[ \frac{e^{-\lambda}\lambda^k}{k!} \f]
+    /// \note The algorithm is taken from the book of Donald E. Knuth titled
+    /// ''Seminumerical Algorithms'' (1969). Its running time is linear in the
+    /// return value.
+    
+    int poisson(double lambda)
+    {
+      const double l = std::exp(-lambda);
+      int k=0;
+      double p = 1.0;
+      do {
+        k++;
+        p*=real<double>();
+      } while (p>=l);
+      return k-1;
+    }  
+      
     ///@}