ASA121
The Trigamma Function

ASA121 is a FORTRAN90 library, using double precision arithmetic, which evaluates the trigamma function.

ASA121 is Applied Statistics Algorithm 121. Source code for many Applied Statistics Algorithms is available through STATLIB.

Related Data and Programs:

ASA103 is a FORTRAN90 library which evaluates the digamma function.

ASA121 is also available in a C++ version and a FORTRAN77 version and a MATLAB version.

TEST_VALUES is a FORTRAN90 library which contains sample values for a number of special functions.

Reference:

1. BE Schneider,
   Algorithm AS 121: Trigamma Function,
   Applied Statistics,
   Volume 27, Number 1, 1978, pages 97-99.

Source Code:

• asa121.f90, the source code.
• asa121.csh, commands to compile the source code.

Examples and Tests:

• asa121_prb.f90, a sample calling program.
• asa121_prb.csh, commands to compile and run the sample program.
• asa121_prb_output.txt, the output file.

List of Routines:

• TIMESTAMP prints out the current YMDHMS date as a timestamp.
• TRIGAM calculates trigamma(x) = d**2 log(gamma(x)) / dx**2
• TRIGAMMA_VALUES returns some values of the TriGamma function.

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