Function special::inc_gamma
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pub fn inc_gamma(x: f64, p: f64) -> f64
Compute the regularized lower incomplete gamma function.
The formula is as follows:
γ(x, p) 1 x
P(x, p) = ------- = ---- ∫ t^(p-1) e^(-t) dt
Γ(p) Γ(p) 0
where γ is the incomplete lower gamma function, and Γ is the complete gamma function.
The code is based on a C implementation by John Burkardt. The original algorithm was published in Applied Statistics and is known as Algorithm AS 239.