Geometric probability distribution function.
Geometric(g,b)
Generates a random variate following the Geometric probability distribution with probabitity b.
The pseudo-code algorithm used for this distribution is:
1. Set i = 0.
2. Generate u as U(0,1).
3. If u &le b, return i. Otherwise i=i+1 and go back to 2.
(u,g) := Geometric(g,0.5);
function Geometric extends Var; end Geometric;