Function: incgam
Section: transcendental
C-Name: incgam0
Prototype: GGDGp
Help: incgam(s,x,{g}): incomplete gamma function. g is optional and is the
 precomputed value of gamma(s).
Doc: incomplete gamma function $\int_{x}^{\infty} e^{-t}t^{s-1}\,dt$,
 extended by
 analytic continuation to all complex $x, s$ not both $0$. The relative error
 is bounded in terms of the precision of $s$ (the accuracy of $x$ is ignored
 when determining the output precision). When $g$ is given, assume that
 $g=\Gamma(s)$. For small $|x|$, this will speed up the computation.
Variant: Also available is \fun{GEN}{incgam}{GEN s, GEN x, long prec}.
