Weibull probability distribution function.
Weibull(g,alpha,beta)
Generates a random variate following the Weibull probability distribution, with parameters alpha and beta.
The pseudo-code algorithm used for this distribution is:
1. Generate u as U(0,1)
2. Return x = alpha*((-ln(1-u))^(1/beta))
(u,g) := Weibull(g,0.4,0.8);
function Weibull extends Var; end Weibull;