public void ValidateCumulativeDistribution(int shape, double invScale, double x, double cdf)
{
var n = new Erlang(shape, invScale);
AssertHelpers.AlmostEqual(cdf, n.CumulativeDistribution(x), 14);
AssertHelpers.AlmostEqual(cdf, Erlang.CDF(shape, invScale, x), 14);
}