where 𝛤(𝛽) is the Gamma function:
Range 0 ≤ 𝑥 - 𝜃 < ∞
Scale parameter, 𝛼 > 0
Shape parameter, 𝛽 > 0
Threshold parameter 𝜃 < 𝑚𝑖𝑛(𝑥)