Cdigamma Digamma Digamma_sub Polygamma Polygamma_sub Trigamma Trigamma_sub

Digamma_sub() Sub Digamma_sub ( Ret As  Double, X As  Double, Optional Info As  Long  ) Digamma (or psi) function ψ(x) (Subroutine version) Purpose Computes the digamma (or psi) function ψ(x), where x is not 0, -1, -2, ... ψ(x) = d/dx ln(Γ(x)) = Γ'(x)/Γ(x) Parameters [out] Ret Digamma (or psi) function ψ(x). [in] X Argument x. (X <> 0 and X <> a negative integer) [out] Info (Optional) = 0: Successful exit. = -1: The argument X had an illegal value. (X = 0 or a negative integer) = 1: Floating point range error. Reference boost/math/special_functions