Cdigamma Digamma Polygamma Trigamma

Trigamma() Function Trigamma ( X As  Double, Optional Info As  Long  ) Trigamma function ψ1(x) Purpose This routine computes the trigamma function ψ1(x), where x is not 0, -1, -2, ... ψ1(x) = dψ(x)/dx = d2/dx2 ln(Γ(x)) Returns Double Trigamma function ψ1(x). Parameters [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