uigamma

uigamma(a, x) returns the regularized upper incomplete gamma function Q(a, x), NIST DLMF eq 8.2.4 For the complementary lower incomplete gamma function P(a,x), see igamma. Q(a, x) + P(a, x) = 1.

The current implementation is from the Cephes library (Moshier 2000). The domain is restricted to real a>0, real x>=0.