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Journal Articles Bulletin des Sciences Mathématiques Year : 2021

Some Remarks on the Location of Non-Asymptotic Zeros of Whittaker and Kummer Hypergeometric Functions

Abstract

This paper focuses on the location of the non-asymptotic zeros of Whittaker and Kummer confluent hypergeometric functions. Based on a technique by E. Hille for the analysis of solutions of some second-order ordinary differential equations, we characterize the sign of the real part of zeros of Whittaker and Kummer functions and provide estimates on the regions of the complex plane where those zeros can be located. Our main result is a correction of a previous statement by G. E. Tsvetkov whose propagation has induced mistakes in the literature. In particular, we review some results of E. B. Saff and R. S. Varga on the error of Padé's rational approximation of the exponential function, which are based on the latter.
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Dates and versions

hal-03250426 , version 1 (04-06-2021)
hal-03250426 , version 2 (17-06-2021)

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Islam Boussaada, Guilherme Mazanti, Silviu-Iulian Niculescu. Some Remarks on the Location of Non-Asymptotic Zeros of Whittaker and Kummer Hypergeometric Functions. Bulletin des Sciences Mathématiques, 2021, 174, Paper No. 103093, 12 pp. ⟨10.1016/j.bulsci.2021.103093⟩. ⟨hal-03250426v2⟩
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