; docformat = 'rst' ;+ ; Calculate a mathematical permutation. ; ; :Returns: ; long64 ; ; :Params: ; m : in, required, type=integer ; number of items ; n : in, required, type=integer ; size of permutation ;- function mg_permutation, m, n compile_opt strictarr return, round(exp(lngamma(m + 1.D) - lngamma(m - n + 1.D)), /l64) end