(PECL stats:1.0.0-1.0.2)
stats_rand_gen_beta — Generates beta random deviate
Returns a random deviate from the beta distribution with parameters A and B. The density of the beta is x^(a-1) * (1-x)^(b-1) / B(a,b) for 0 < x <. Method R. C. H. Cheng.