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 Pad{é}'s rational approximation of the exponential function, which are based on the latter.

References in corpus (1)

• Multiplicity-induced-dominancy for delay-differential equations of retarded type

Cited by in corpus (4)

• The generic multiplicity-induced-dominancy property from retarded to neutral delay-differential equations: When delay-systems characteristics meet the zeros of Kummer functions
• Stability, Delays and Multiple Characteristic Roots in Dynamical Systems: A Guided Tour
• MID Property for Delay Systems: Insights on Spectral Values with Intermediate Multiplicity
• Padé Approximation and Hypergeometric Functions: A Missing Link with the Spectrum of Delay-Differential Equations