# HG changeset patch
# User alpar
# Date 1171976482 0
# Node ID b59a17034ffaa8383f4a4ce986ec8ffd3a174aea
# Parent  134639e6ea45d5eab7c69bf926b35d8c877db8f2
Some two dimensional random distribution added.
They should be revised.

diff -r 134639e6ea45 -r b59a17034ffa lemon/random.h
--- a/lemon/random.h	Tue Feb 20 12:55:37 2007 +0000
+++ b/lemon/random.h	Tue Feb 20 13:01:22 2007 +0000
@@ -69,6 +69,7 @@
 #include <ctime>
 #include <cmath>
 
+#include <lemon/dim2.h>
 ///\ingroup misc
 ///\file
 ///\brief Mersenne Twister random number generator
@@ -742,11 +743,66 @@
     ///
     double exponential(double lambda=1.0)
     {
-      return -log(real<double>())/lambda;
+      return -std::log(real<double>())/lambda;
     }
 
     ///@}
     
+    ///\name Two dimensional distributions
+    ///
+
+    ///@{
+    
+    /// Uniform distribution on the full unit circle.
+    dim2::Point<double> ball2() 
+    {
+      double V1,V2;
+      do {
+	V1=2*real<double>()-1;
+	V2=2*real<double>()-1;
+	
+      } while(V1*V1+V2*V2>=1);
+      return dim2::Point<double>(V1,V2);
+    }
+    /// A kind of two dimensional Gauss distribution
+
+    /// This function provides a turning symmetric two-dimensional distribution.
+    /// Both coordinates are of standard normal distribution, but they are not
+    /// independent.
+    ///
+    /// \note The coordinates are the two random variables provided by
+    /// the Box-Muller method.
+    dim2::Point<double> gauss2()
+    {
+      double V1,V2,S;
+      do {
+	V1=2*real<double>()-1;
+	V2=2*real<double>()-1;
+	S=V1*V1+V2*V2;
+      } while(S>=1);
+      double W=std::sqrt(-2*std::log(S)/S);
+      return dim2::Point<double>(W*V1,W*V2);
+    }
+    /// A kind of two dimensional exponential distribution
+
+    /// This function provides a turning symmetric two-dimensional distribution.
+    /// The x-coordinate is of conditionally exponential distribution
+    /// with the condition that x is positive and y=0. If x is negative and 
+    /// y=0 then, -x is of exponential distribution. The same is true for the
+    /// y-coordinate.
+    dim2::Point<double> exponential2() 
+    {
+      double V1,V2,S;
+      do {
+	V1=2*real<double>()-1;
+	V2=2*real<double>()-1;
+	S=V1*V1+V2*V2;
+      } while(S>=1);
+      double W=-std::log(S)/S;
+      return dim2::Point<double>(W*V1,W*V2);
+    }
+
+    ///@}    
   };