This is the tgamma_lower from the boost library
Details
The lowergamma function is given by:
$$lowergamma(a, z) = \int_{0}^{z}t^{a-1}\cdot e^{-t} dt$$
See also
Other Special functions:
boxCox(),
delay(),
erf(),
gammap(),
gammapDer(),
gammapInv(),
gammaq(),
gammaqInv(),
logit(),
mexpit(),
mlogit(),
phi(),
phiU(),
probit(),
uppergamma()
