PR: 29419 Added an implementation of regularized gamma function, Q(a, x) = 1 - P(a,x), based on a continued fraction. This converges much faster for the large x case. I added the example submitted by Scott as a test case and ran all the test cases with everything passing.
jakarta/commons/proper/math/trunk/src/java/org/apache/commons/math/special/Gamma.java