ASA109 is a MATLAB library which "inverts" the incomplete Beta function by Cran, Martin and Thomas.
Given a value of the incomplete Beta function, it can determine the argument that produced that value.
ASA109 is Applied Statistics Algorithm 109. Source code for many Applied Statistics Algorithms is available through STATLIB.
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
ASA109 is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.
ASA063, a MATLAB library which evaluates the incomplete Beta function.
ASA226, a MATLAB library which evaluates the CDF of the noncentral Beta distribution.
ASA310, a MATLAB library which computes the CDF of the noncentral Beta distribution.
BETA_NC, a MATLAB library which evaluates the CDF of the noncentral Beta distribution.
TEST_VALUES, a MATLAB library which stores a few values of various mathematical functions.
TOMS179, a MATLAB library which evaluates the incomplete Beta function.
TOMS708, a FORTRAN90 library which evaluates the incomplete Beta function.
Original FORTRAN77 version by GW Cran, KJ Martin, GE Thomas; MATLAB version by John Burkardt.
You can go up one level to the MATLAB source codes.