Approximation in Hankel Sobolev Space by Circular prolate spheroidal series

Abstract

Recently, with the progress of science and the characteristic properties that distinguish the Slepian system called Prolate spheroidal wave functions from the others orthonormal systems, it became clear its important contributions in several areas such as mathematical statistics, signal processing, numerical analysis etc...The main issue of this work is to establish the convergence quality of the truncated error of a function $f$ from the Hankel Sobolev space $\mathcal{H}_{\alpha}^r$, $r > 0$ and $\alpha\geq -1/2$, by a generalized prolate spheroidal wave functions basis in $L^2$ norm. In the meantime, we will create two uniform approximations of the previous system by two special functions, the first is a Bessel function type and the second is a modified Jacobi polynomial. Furthermore, using the fact that the generalized PSWFs are the eigenfunctions of a Sturm Liouville operator, we will improve a new bound of the associated eigenvalues. The generalized prolate basis we consider here is the circular prolate spheroidal wave function (CPSWFs), called also Hankel prolate, introduced by D. Slepian in 1964, denoted by $\vp$, $c > 0$. The Hankel prolate covers the classical PSWFs $(\alpha=\pm1/2)$ for which corresponding results have been established previously by many authors.