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