public void ValidateInverseCumulativeDistribution(int shape, double invScale, double x, double cdf)
 {
     var gamma = new Gamma(shape, invScale);
     Assert.That(gamma.InverseCumulativeDistribution(cdf), Is.EqualTo(x).Within(10));
     Assert.That(Gamma.InvCDF(shape, invScale, cdf), Is.EqualTo(x).Within(10));
 }