ASA103
The Digamma or Psi Function

ASA103 is a FORTRAN90 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 MATLAB 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 FORTRAN90 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:

• asa103.f90, the source code.
• asa103.csh, commands to compile the source code.

Examples and Tests:

• asa103_prb.f90, a sample calling program.
• asa103_prb.csh, commands to compile and run the sample program.
• asa103_prb_output.txt, the output file.

List of Routines:

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

You can go up one level to the FORTRAN90 source codes.