Hostname: page-component-77c89778f8-m8s7h Total loading time: 0 Render date: 2024-07-16T11:14:29.530Z Has data issue: false hasContentIssue false

Wiener amalgams and pointwise summability of Fourier transforms and Fourier series

Published online by Cambridge University Press:  26 April 2006

HANS G. FEICHTINGER
Affiliation:
Numerical Harmonic Analysis Group, Faculty of Mathematics, University of Vienna, Nordbergstraße 15, A-1090 Vienna, Austria. e-mail: hans.feichtinger@univie.ac.at
FERENC WEISZ
Affiliation:
Department of Numerical Analysis, Eötvös L. University, Pázmány P. sétány 1/C., H-1117 Budapest, Hungary. e-mail: weisz@ludens.elte.hu

Abstract

This paper provides a fairly general approach to summability questions for multi-dimensional Fourier transforms. It is based on the use of Wiener amalgam spaces $W(L_p,\ell_q)({\mathbb R}^d)$, Herz spaces and weighted versions of Feichtinger's algebra and covers a wide range of concrete special cases (20 of them are listed at the end of the paper). It is proved that under some conditions the maximal operator of the $\theta$-means $\sigma_T^\theta f$ can be estimated pointwise by the Hardy–Littlewood maximal function. From this it follows that $\sigma_T^\theta f \,{\to}\, f$ a.e. for all $f\in W(L_1,\ell_\infty)({\mathbb R}^d)$, hence $f\in L_p({\mathbb R}^d)$ for any $1\leq p\leq \infty$. Moreover, $\sigma_T^\theta f(x)$ converges to $f(x)$ at each Lebesgue point of $f\in L_1({\mathbb R}^d)$ (resp. $f\in W(L_1,\ell_\infty)({\mathbb R}^d)$) if and only if the Fourier transform of $\theta$ is in a suitable Herz space. In case $\theta$ is in a Besov space or in a weighted Feichtinger's algebra or in a Sobolev-type space then the a.e. convergence is obtained. Some sufficient conditions are given for $\theta$ to be in the weighted Feichtinger's algebra. The same results are presented for multi-dimensional Fourier series.

Type
Research Article
Copyright
2006 Cambridge Philosophical Society

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)