cdigamma cdigamma_sub digamma polygamma trigamma

digamma() double digamma ( double  x ) Digamma (or psi) function ψ(x) Purpose digamma 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) Returns Digamma (or psi) function ψ(x). Parameters [in] x Argument x. (x != negative integer, x != 0) Error handling If x is negative integer or 0, domain error (EDOM) occurs. Range error (ERANGE) may occur. Reference boost/math/special_functions