cdigamma cdigamma_sub digamma polygamma trigamma

trigamma() double trigamma ( double  x ) Trigamma function ψ1(x) Purpose trigamma computes the trigamma function ψ1(x), where x is not 0, -1, -2, ... ψ1(x) = dψ(x)/dx = d2/dx2 ln(Γ(x)) Returns Trigamma function ψ1(x). Parameters [in] x Argument x. (x != negative integer, x != 0) Error handling If x is negative integer or 0, inf is returned and range error (ERANGE) occurs. Other range error (ERANGE) may occur. Reference boost/math/special_functions