Numerical Representations of the Incomplete Gamma Function of Complex-Valued Argument

Various approaches to the numerical representation of the incomplete Gamma function γ(m+1/2,z) for complex arguments z and non-negative small integer indices m are compared with respect to numerical fitness (accuracy and speed). We consider power series, Laurent series, classical numerical methods of sampling the basic integral representation, and others not yet covered by the literature. The most suitable scheme is the construction of Taylor expansions around nodes of a regular, fixed grid in the z-plane, which stores a static matrix of higher derivatives. This is the obvious extension to a procedure that is in common use for real-valued z.

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