ASA103
The Digamma or Psi Function

ASA103 is a MATLAB library 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.

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