1. Algorithm 610: A Portable FORTRAN Subroutine for Derivatives of the Psi Function
2. ABRAMOWITZ M. AND STEGUN I.A. 1964. Handbook of Mathematical Functions. U.S. Govermnent Printing Office Washington D.C.]] ABRAMOWITZ M. AND STEGUN I.A. 1964. Handbook of Mathematical Functions. U.S. Govermnent Printing Office Washington D.C.]]
3. ADIFOR-- Generative derivative codes from Fortran programs. Sci;BISCHOF A.;Program.,1992
4. Certification of Algorithm 708
5. CHAR B. W. GEDDES K. O. GONNET G. a. MONAGAN M. B. AND WATT S. M. 1988. MAPLE Reference Manual. 5th ed. WATCOM Publications Waterloo Ontario.]] CHAR B. W. GEDDES K. O. GONNET G. a. MONAGAN M. B. AND WATT S. M. 1988. MAPLE Reference Manual. 5th ed. WATCOM Publications Waterloo Ontario.]]