x = qbeta(p,a,b) Input p probability a,b positive reals, parameters of the beta distribution (p,a,b can be scalar or matrix with common size) Output for each element of p, F is an ``inverse'' of the beta cumulative distribution function with parameter a and b (the beta density is : x--> x.^(a-1) .* (1-x).^(b-1) ./ beta(a,b)1_{0<x<1})