Polygamma Function

Function: double gsl_sf_psi_n (int m, double x)

Function: int gsl_sf_psi_n_e (int m, double x, gsl_sf_result * result)

These routines compute the polygamma function @c{$\psi^{(m)}(x)$} @math{\psi^{(m)}(x)} for @math{m >= 0}, @math{x > 0}.