Evaluate an incomplete gamma function:
$$\gamma(a, x) = \int_{0}^{x} t^{a-1} e^{-t}dt,$$
using SLATEC dgami in https://netlib.org/slatec/.
When (\(x > 0\) and \(a \ge 0\)) or (\(x \ge 0\) and \(a > 0\)),
compute the result, otherwise the value is NaN.
Arguments
- a
A positive numeric vector.
- x
A nonnegative numeric vector with same length as
a. length.