From 600aa2ec161ce3260367faece5ab4f9798d55471 Mon Sep 17 00:00:00 2001
From: Raj Bhattacharjea <raj.b@gatech.edu>
Date: Wed, 18 Jul 2007 17:43:45 -0400
Subject: [PATCH] Added Triangularly distributed random variables

---
 src/core/random-variable.cc | 37 +++++++++++++++++++++++++++++++
 src/core/random-variable.h  | 44 +++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/src/core/random-variable.cc b/src/core/random-variable.cc
index 824778c29..f93404fda 100644
--- a/src/core/random-variable.cc
+++ b/src/core/random-variable.cc
@@ -684,6 +684,43 @@ double LogNormalVariable::GetSingleValue (double mu, double sigma)
   return z;
 }
 
+//-----------------------------------------------------------------------------
+//-----------------------------------------------------------------------------
+// TriangularVariable methods
+TriangularVariable::TriangularVariable() 
+  : m_min(0), m_max(1), m_mode(0.5) { }
+  
+TriangularVariable::TriangularVariable(double s, double l, double mean) 
+  : m_min(s), m_max(l), m_mode(3.0*mean-s-l) { }
+  
+TriangularVariable::TriangularVariable(const TriangularVariable& c) 
+  : RandomVariable(c), m_min(c.m_min), m_max(c.m_max), m_mode(c.m_mode) { }
+
+double TriangularVariable::GetValue()
+{
+  double u = m_generator->RandU01();
+  if(u <= (m_mode - m_min) / (m_max - m_min) )
+    return m_min + sqrt(u * (m_max - m_min) * (m_mode - m_min) );
+  else
+    return m_max - sqrt( (1-u) * (m_max - m_min) * (m_max - m_mode) );
+}
+
+RandomVariable* TriangularVariable::Copy() const
+{
+  return new TriangularVariable(*this);
+}
+
+double TriangularVariable::GetSingleValue(double s, double l, double mean)
+{
+  double mode = 3.0*mean-s-l;
+  double u = m_static_generator->RandU01();
+  if(u <= (mode - s) / (l - s) )
+    return s + sqrt(u * (l - s) * (mode - s) );
+  else
+    return l - sqrt( (1-u) * (l - s) * (l - mode) );
+}
+
+
 }//namespace ns3
 
 
diff --git a/src/core/random-variable.h b/src/core/random-variable.h
index 1007e878d..7759ea157 100644
--- a/src/core/random-variable.h
+++ b/src/core/random-variable.h
@@ -737,6 +737,50 @@ private:
   double m_sigma;
 };
 
+/**
+ * \brief Triangularly Distributed random var
+ * \ingroup randomvariable
+ * 
+ * This distribution is a triangular distribution.  The probablility density
+ * is in the shape of a triangle.
+ */
+class TriangularVariable : public RandomVariable {
+public:
+  /**
+   * Creates a triangle distribution random number generator in the
+   * range [0.0 .. 1.0), with mean of 0.5
+   */
+  TriangularVariable();
+
+  /**
+   * Creates a triangle distribution random number generator with the specified
+   * range
+   * \param s Low end of the range
+   * \param l High end of the range
+   * \param mean mean of the distribution
+   */
+  TriangularVariable(double s, double l, double mean);
+
+  TriangularVariable(const TriangularVariable& c);
+  
+  /**
+   * \return A value from this distribution
+   */
+  virtual double GetValue();
+  virtual RandomVariable*  Copy() const;
+public:
+  /**
+   * \param s Low end of the range
+   * \param l High end of the range
+   * \return A triangularly distributed random number between s and l
+   */
+  static double GetSingleValue(double s, double l, double mean);
+private:
+  double m_min;
+  double m_max;
+  double m_mode;  //easier to work with the mode internally instead of the mean
+                  //they are related by the simple: mean = (min+max+mode)/3
+};
 
 }//namespace ns3
 #endif