/// <summary>
/// Returns the probability distribution function.
/// </summary>
public double pdf(double x)
{
if (x < 0)
{
throw new ArgumentException();
}
if (x == 0)
{
if (alpha == 1.0)
{
return(1.0 / lambda);
}
else
{
return(0.0);
}
}
if (alpha == 1.0)
{
return(System.Math.Exp(-x / lambda) / lambda);
}
return(System.Math.Exp((alpha - 1.0) * System.Math.Log(x / lambda) - x / lambda - Fun.LogGamma(alpha)) / lambda);
}
