Extended the chisquare distribution to support the generation of samples for non-integer dof.

src/Numerics/Distributions/Continuous/ChiSquare.cs

@@ -273,6 +273,9 @@ namespace MathNet.Numerics.Distributions
         /// <param name="dof">The degrees of freedom.</param>
         /// <returns>a random number from the distribution.</returns>
         private static double DoSample(Random rnd, double dof)
+        {
+            //Use the simple method if the dof is an integer anyway
+            if (Math.Floor(dof) == dof && dof < Int32.MaxValue)
             {
                 double sum = 0;
                 var n = (int)dof;
@@ -280,9 +283,12 @@ namespace MathNet.Numerics.Distributions
                 {
                     sum += Math.Pow(Normal.Sample(rnd, 0.0, 1.0), 2);
                 }
-
                 return sum;
             }
+            //Call the gamma function (see http://en.wikipedia.org/wiki/Gamma_distribution#Specializations
+            //for a justification)
+            return Gamma.Sample(rnd, dof / 2.0, .5);
+        }
 
         /// <summary>
         /// Generates a sample from the <c>ChiSquare</c> distribution.