Algorithm 708: Significant digit computation of the incomplete beta function ratios
Armido R. Didonato, Alfred H. Morris · ACM Transactions on Mathematical Software · 1992
An algorithm is given for evaluating the incomplete beta function ratio I x (a,b) and its complement 1 - I x (a,b) . A new continued fraction and a new asymptotic series are used with classical results. A transportable Fortran subroutine based on this algorithm is currently in use. It is accurate to 14 significant digits when precision is not restricted by inherent error.