From GeoGebra Manual
- InverseGamma( <Alpha>, <Beta>, <Probability> )
- Computes the inverse of cumulative distribution function of gamma distribution at probability p, where the gamma distribution is given by parameters Alpha and Beta.
- In other words, finds t such that P(X ≤ t) = p, where X is random variable with gamma distribution.
- Probability p must be from [0,1].