(PECL stats:1.0.0-1.0.2)
stats_rand_gen_gamma — Generates random deviates from a gamma distribution
Generates random deviates from the gamma distribution whose density is (A**R)/Gamma(R) * X**(R-1) * Exp(-A*X).
location parameter of Gamma distribution (a > 0).
shape parameter of Gamma distribution (r > 0).