toms443, a FORTRAN90 code which evaluates Lambert's W function. This is a version of ACM TOMS algorithm 443, by Fritsch, Shafer and Crowley.
Lambert's W function W(X) satisfies the equation
W(x) * exp ( W(x) ) = x
The text of many ACM TOMS algorithms is available online through ACM: https://calgo.acm.org/ or NETLIB: https://www.netlib.org/toms/index.html.
The computer code and data files made available on this web page are distributed under the MIT license
toms443 is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version.
TEST_VALUES, a FORTRAN90 code which contains routines which return sample values of various functions, including the modified beta function, and the logarithm of the gamma function.
TOMS743, a FORTRAN90 code which evaluates Lambert's W function. This is a version of ACM TOMS algorithm 743, by Barry, Barry and Culligan-Hensley.