public void ValidateInverseCumulativeDistribution(double lambda, double x)
{
var n = new Exponential(lambda);
Assert.AreEqual(x, n.InverseCumulativeDistribution(1.0 - Math.Exp(-lambda * x)));
Assert.AreEqual(x, Exponential.InvCDF(lambda, 1.0 - Math.Exp(-lambda * x)));
}