Calculates the inverse of the cumulative GAMMADIST function.
Syntax:
GAMMAINV(p, α, β)
The gamma distribution is a family of continuous probability distributions, with two controlling parameters α and β.
GAMMAINV returns the value n, such that GAMMADIST(n, α, β, 1) is p.
Example:
GAMMAINV(0.86, 1, 1)
returns approximately 2.