Digamma Function

Function: double gsl_sf_psi_int (int n)

Function: int gsl_sf_psi_int_e (int n, gsl_sf_result * result)

These routines compute the digamma function @math{\psi(n)} for positive integer n. The digamma function is also called the Psi function.

Function: double gsl_sf_psi (double x)

Function: int gsl_sf_psi_e (double x, gsl_sf_result * result)

These routines compute the digamma function @math{\psi(x)} for general @math{x}, @math{x \ne 0}.

Function: double gsl_sf_psi_1piy (double y)

Function: int gsl_sf_psi_1piy_e (double y, gsl_sf_result * result)

These routines compute the real part of the digamma function on the line @math{1+i y}, @math{Re[\psi(1 + i y)]}.