From db4a70cbe4ac4eb5098fbe8b0d9240ced9c4f145 Mon Sep 17 00:00:00 2001
From: Jurgen Van Gael <jurgen.vangael@gmail.com>
Date: Sun, 20 Sep 2009 17:29:49 +0800
Subject: [PATCH] Enabled Beta entropy test.

Signed-off-by: jvangael <jurgen.vangael@gmail.com>

Signed-off-by: jvangael <jurgen.vangael@gmail.com>
---
 src/Numerics/Distributions/Continuous/Beta.cs | 32 ++++++++++++++++---
 .../DistributionTests/Continuous/BetaTests.cs | 10 +++---
 2 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/src/Numerics/Distributions/Continuous/Beta.cs b/src/Numerics/Distributions/Continuous/Beta.cs
index 69be2966..ad48a83a 100644
--- a/src/Numerics/Distributions/Continuous/Beta.cs
+++ b/src/Numerics/Distributions/Continuous/Beta.cs
@@ -36,7 +36,14 @@ namespace MathNet.Numerics.Distributions
     /// Implements the Beta distribution. For details about this distribution, see 
     /// <a href="http://en.wikipedia.org/wiki/Beta_distribution">Wikipedia - Beta distribution</a>.
     /// </summary>
-    /// <remarks><para>The distribution will use the <see cref="System.Random"/> by default. 
+    /// <remarks>
+    /// <para>There are a few special cases for the parameterization of the Beta distribution. When both
+    /// shape parameters are positive infinity, the Beta distribution degenerates to a point distribution
+    /// at 0.5. When one of the shape parameters is positive infinity, the distribution degenerates to a point
+    /// distribution at the positive infinity. When both shape parameters are 0.0, the Beta distribution 
+    /// degenerates to a Bernoulli distribution with parameter 0.5. When one shape parameter is 0.0, the
+    /// distribution degenerates to a point distribution at the non-zero shape parameter.</para>
+    /// <para>The distribution will use the <see cref="System.Random"/> by default. 
     /// Users can get/set the random number generator by using the <see cref="RandomSource"/> property.</para>
     /// <para>The statistics classes will check all the incoming parameters whether they are in the allowed
     /// range. This might involve heavy computation. Optionally, by setting Control.CheckDistributionParameters
@@ -217,10 +224,25 @@ namespace MathNet.Numerics.Distributions
         {
             get
             {
-                return SpecialFunctions.BetaLn(_shapeA, _shapeB)
-                       - ((_shapeA - 1.0) * SpecialFunctions.DiGamma(_shapeA))
-                       - ((_shapeB - 1.0) * SpecialFunctions.DiGamma(_shapeB))
-                       + ((_shapeA + _shapeB - 2.0) * SpecialFunctions.DiGamma(_shapeA + _shapeB));
+                if (Double.IsPositiveInfinity(_shapeA) || Double.IsPositiveInfinity(_shapeB))
+                {
+                    return 0.0;
+                }
+                else if (_shapeA == 0.0 && _shapeB == 0.0)
+                {
+                    return -Math.Log(0.5);
+                }
+                else if (_shapeA == 0.0 || _shapeB == 0.0)
+                {
+                    return 0.0;
+                }
+                else
+                {
+                    return SpecialFunctions.BetaLn(_shapeA, _shapeB)
+                           - ((_shapeA - 1.0) * SpecialFunctions.DiGamma(_shapeA))
+                           - ((_shapeB - 1.0) * SpecialFunctions.DiGamma(_shapeB))
+                           + ((_shapeA + _shapeB - 2.0) * SpecialFunctions.DiGamma(_shapeA + _shapeB));
+                }
             }
         }
 
diff --git a/src/UnitTests/DistributionTests/Continuous/BetaTests.cs b/src/UnitTests/DistributionTests/Continuous/BetaTests.cs
index b6585b0d..283fa501 100644
--- a/src/UnitTests/DistributionTests/Continuous/BetaTests.cs
+++ b/src/UnitTests/DistributionTests/Continuous/BetaTests.cs
@@ -139,10 +139,10 @@ namespace MathNet.Numerics.UnitTests.DistributionTests
             AssertEx.AreEqual<double>(mean, n.Mean);
         }
 
-        [Test, Ignore("Depending on Special Functions")]
-        [Row(0.0, 0.0, 0.5)]
-        [Row(0.0, 0.1, 0.1)]
-        [Row(1.0, 0.0, 1.0)]
+        [Test]
+        [Row(0.0, 0.0, 0.693147180559945309417232121458176568075500134360255)]
+        [Row(0.0, 0.1, 0.0)]
+        [Row(1.0, 0.0, 0.0)]
         [Row(1.0, 1.0, 0.0)]
         [Row(9.0, 1.0, -1.3083356884473304939016015849561625204060922267565917)]
         [Row(5.0, 100.0, -2.5201623187602743679459255108827601222133603091753153)]
@@ -153,7 +153,7 @@ namespace MathNet.Numerics.UnitTests.DistributionTests
         public void ValidateEntropy(double a, double b, double entropy)
         {
             var n = new Beta(a, b);
-            AssertEx.AreEqual<double>(entropy, n.Entropy);
+            AssertHelpers.AlmostEqual(entropy, n.Entropy, 14);
         }
 
         [Test]