GNU Scientific Library Reference Manual - Third Edition (v1.12) by M. Galassi, J. Davies, J. Theiler, B. Gough, G. Jungman, P. Alken, M. Booth, F. Rossi Paperback (6"x9"), 592 pages, 60 figures ISBN 0954612078 RRP £24.95 ($39.95) Get a printed copy>>>

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7.28.1 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 \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 \psi(x) for general x, 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 1+i y, \Re[\psi(1 + i y)].