Cdigamma Digamma Polygamma Trigamma

Polygamma() Function Polygamma ( X As  Double, N As  Long, Optional Info As  Long  ) Polygamma function ψn(x) Purpose This routine computes the polygamma function ψn(x), where x is not 0, -1, -2, ... ψn(x) = dnψ(x)/dxn = d(n+1)/dx(n+1) ln(Γ(x)) Returns Double Polygamma function ψn(x). Parameters [in] X Argument x. (X <> 0 and X <> a negative integer) [in] N Argument n. (N >= 0) [out] Info (Optional) = 0: Successful exit. = -1: The argument X had an illegal value. (X = 0 or a negative integer) = -2: The argument N had an illegal value. (N < 0) = 1: Floating point range error. Reference boost/math/special_functions