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Distributional Point Values and Convergence of Fourier Series and Integrals
Authors:Jasson Vindas  Ricardo Estrada
Affiliation:(1) Mathematics Department, Louisiana State University, Baton Rouge, Louisiana, USA
Abstract:In this article we show that the distributional point values of a tempered distribution are characterized by their Fourier transforms in the following way: If $finmathcal{S}^{prime}left(mathbb{R}right)$ and $x_{0}inmathbb{R}$ , and $widehat{f}$ is locally integrable, then $f(x_{0})=gamma $ distributionally if and only if there exists k such that $frac{1}{2pi}lim_{xrightarrowinfty}int_{-x}^{ax} hat{f}(t)e^{-ix_{0}t},mathrm{d}t=gamma  (mathrm{C},k),$ , for each a > 0, and similarly in the case when $widehat{f}$ is a general distribution. Here $(mathrm{C},k)$ means in the Cesaro sense. This result generalizes the characterization of Fourier series of distributions with a distributional point value given in [5] by $lim_{xrightarrowinfty}sum_{-xleq nleq ax}a_{n}e^{inx_{0}}=gamma (mathrm{C},k),$ . We also show that under some extra conditions, as if the sequence $left{a_{n}right}  _{n=-infty}^{infty}$ belongs to the space $l^{p}$ for some $pinlbrack1,infty)$ and the tails satisfy the estimate $sum_{leftvert nrightvert geq N}^{infty}leftvert a_{n}rightvert ^{p}=Oleft(N^{1-p}right)  $ , as $Nrightarrowinfty$ , the asymmetric partial sums converge to $gamma$ . We give convergence results in other cases and we also consider the convergence of the asymmetric partial integrals. We apply these results to lacunary Fourier series of distributions.
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