asa103, a C++ code which evaluates the digamma or psi function; this is a version of Applied Statistics Algorithm 103, by Jose Bernardo.
The information on this web page is distributed under the MIT license.
asa103 is available in a C version and a C++ version and a Fortran90 version and a MATLAB version and an Octave version and a Python version.
asa121, a C++ code which evaluates the trigamma function.
fn, a C++ code which approximates elementary and special functions using Chebyshev polynomials; functions include Airy, Bessel I, Bessel J, Bessel K, Bessel Y, beta, confluent hypergeometric, cosine integral, Dawson's integral, digamma (psi), error, exponential integral, gamma, hyperbolic cosine integral, hyperbolic sine integral, incomplete gamma, log gamma, logarithmic integral, Pochhammer, psi, sine integral, Spence; by Wayne Fullerton.
test_values, a C++ code 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; This version by John Burkardt.