This function returns a random variate from the gamma distribution. The distribution function is,
for \(x > 0\).
The gamma distribution with an integer parameter a is known as the Erlang distribution.
The variates are computed using the Marsaglia-Tsang fast gamma method.
This function returns a gamma variate using the algorithms from Knuth (vol 2).
This function computes the probability density \(p(x)\) at \(x\) for a gamma distribution with parameters a and b, using the formula given above.
These functions compute the cumulative distribution functions \(P(x), Q(x)\) and their inverses for the gamma distribution with parameters a and b.