cpp/numeric/random/gamma distribution

Produces random positive floating-point values $x$, distributed according to probability density function:



where $α$ is known as the shape parameter and $β$ is known as the scale parameter. The shape parameter is sometimes denoted by the letter $k$ and the scale parameter is sometimes denoted by the letter $θ$.

For floating-point $α$, the value obtained is the sum of $α$ independent exponentially distributed random variables, each of which has a mean of $β$.

satisfies.