public void RandWishart()
{
// multivariate Gamma
double a = 2.7;
int d = 3;
PositiveDefiniteMatrix mTrue = new PositiveDefiniteMatrix(d, d);
mTrue.SetToIdentity();
mTrue.SetToProduct(mTrue, a);
LowerTriangularMatrix L = new LowerTriangularMatrix(d, d);
PositiveDefiniteMatrix X = new PositiveDefiniteMatrix(d, d);
PositiveDefiniteMatrix m = new PositiveDefiniteMatrix(d, d);
m.SetAllElementsTo(0);
double s = 0;
for (int i = 0; i < nsamples; i++)
{
Rand.Wishart(a, L);
X.SetToProduct(L, L.Transpose());
m = m + X;
s = s + X.LogDeterminant();
}
double sTrue = 0;
for (int i = 0; i < d; i++)
{
sTrue += MMath.Digamma(a - i * 0.5);
}
m.Scale(1.0 / nsamples);
s = s / nsamples;
Console.WriteLine("");
Console.WriteLine("Multivariate Gamma");
Console.WriteLine("-------------------");
Console.WriteLine("m = \n{0}", m);
double dError = m.MaxDiff(mTrue);
if (dError > TOLERANCE)
{
Assert.True(false, String.Format("Wishart({0}) mean: (should be {0}*I), error = {1}", a, dError));
}
if (System.Math.Abs(s - sTrue) > TOLERANCE)
{
Assert.True(false, string.Format("E[logdet]: {0} (should be {1})", s, sTrue));
}
}
