Evaluation of Abramowitz functions in the right half of the complex plane

Zydrunas Gimbutas, Shidong Jiang, Li-Shi Luo

Published 2019-06-28Version 1

A numerical scheme is developed for the evaluation of Abramowitz functions $J_n$ in the right half of the complex plane. For $n=-1,\, \ldots,\, 2$, the scheme utilizes series expansions for $|z|<1$ and asymptotic expansions for $|z|>R$ with $R$ determined by the required precision, and modified Laurent series expansions which are precomputed via a least squares procedure to approximate $J_n$ accurately and efficiently on each sub-region in the intermediate region $1\le |z| \le R$. For $n>2$, $J_n$ is evaluated via a recurrence relation. The scheme achieves nearly machine precision for $n=-1, \ldots, 2$, with the cost about four times of evaluating a complex exponential per function evaluation.