ASA103 is a MATLAB library which evaluates the digamma or psi function, by Jose Bernardo.
ASA103 is Applied Statistics Algorithm 103. Source code for many Applied Statistics Algorithms is available through STATLIB.
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
ASA103 is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version
ASA121, a MATLAB library which evaluates the trigamma function.
SPECFUN, a FORTRAN90 library which computes special functions, including the Psi or Digamma function.
TEST_VALUES, a MATLAB library which contains sample values for a number of distributions.
TOMS708, a FORTRAN90 library which includes routines to evaluate the digamma function.
Original FORTRAN77 version by Jose Bernardo; MATLAB version by John Burkardt.
You can go up one level to the MATLAB source codes.