ASA103
The Digamma or Psi Function

ASA103 is a MATLAB library, using double precision arithmetic, which evaluates the digamma or psi function.

ASA103 is Applied Statistics Algorithm 103. Source code for many Applied Statistics Algorithms is available through STATLIB.

Related Data and Programs:

ASA103 is also available in a C++ version and a FORTRAN77 version and a FORTRAN90 version

ASA121 a library which evaluates the trigamma function.

SPECFUN is a FORTRAN90 library which computes special functions, including the Psi or Digamma function.

TEST_VALUES is a MATLAB library which contains sample values for a number of distributions.

TOMS708 a FORTRAN90 library which includes routines to evaluate the digamma function.

Reference:

1. Jose Bernardo,
   Algorithm AS 103: Psi ( Digamma ) Function,
   Applied Statistics,
   Volume 25, Number 3, 1976, pages 315-317.

Source Code:

• digama.m calculates DIGAMMA ( X ) = d ( LOG ( GAMMA ( X ) ) ) / dX
• psi_values.m returns some values of the Psi or Digamma function for testing.
• timestamp.m prints out the current YMDHMS date as a timestamp.

Examples and Tests:

• asa103_test.m, a sample calling program.
• asa103_test01.m, tests DIGAMA.
• asa103_test_output.txt, the output file.

You can go up one level to the MATLAB source codes.