TOMS179 is a FORTRAN90 library which implements ACM TOMS algorithm 179, for evaluating the modified Beta function.
While the text of many ACM TOMS algorithms is available online through ACM: http://www.acm.org/pubs/calgo or NETLIB: http://www.netlib.org/toms/index.html, many of the early algorithms are not available. This is one of them. I typed it in.
The original algorithm was published in the Algol language. Shortly therafter, a distinct FORTRAN77 algorithm was published as a "remark" to the original algorithm. A few modifications to the FORTRAN77 program were proposed in a subsequent "remark".
call mdbeta ( x, p, q, prob, ier )where
TOMS179 is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version and a Python version.
ASA063, a FORTRAN90 library which evaluates the incomplete Beta function.
ASA109, a FORTRAN90 library which inverts the incomplete Beta function.
ASA226, a FORTRAN90 library which evaluates the CDF of the noncentral Beta distribution.
ASA310, a FORTRAN90 library which computes the CDF of the noncentral Beta distribution.
BETA_NC, a FORTRAN90 library which evaluates the CDF of the noncentral Beta distribution.
DCDFLIB, a FORTRAN90 library which contains routines which evaluate a number of probability density functions, including one based on the Beta function.
PROB, a FORTRAN90 library which contains routines which evaluate a number of probability density functions, including one based on the Beta function.
TEST_VALUES, a FORTRAN90 library which contains routines which return sample values of various functions, including the modified beta function, and the logarithm of the gamma function.
TOMS708, a FORTRAN90 library which evaluates the incomplete beta function.
You can go up one level to the FORTRAN90 source codes.