F = pbeta(x,a,b) Input x matrix (elements between 0 and 1) a,b positive reals, parameters of the beta distribution (x,a,b can be scalar or matrix with common size) Output F for each element of x, F=Prob(X<x) where X is a random variable with beta density : x--> x.^(a-1) .* (1-x).^(b-1) ./ beta(a,b)1_{0<x<1}