MATHEMATICA BOHEMICA, Vol. 139, No. 1, pp. 75-88, 2014

Necessary conditions for the $L^p$-convergence $(0<p<1)$ of single and double trigonometric series

Xhevat Z. Krasniqi, Péter Kórus, Ferenc Móricz

Xhevat Z. Krasniqi, University of Prishtina, Department of Mathematics and Computer Sciences, Avenue Mother Theresa 5, Prishtinë, 10000, Kosovë, e-mail: xheki00@hotmail.com; Péter Kórus (corresponding author), Ferenc Móricz, University of Szeged, Bolyai Institute, Aradi vértanúk tere 1, Szeged, 6720 Hungary, e-mail: korpet@math.u-szeged.hu, moricz@math.u-szeged.hu

Abstract: We give necessary conditions in terms of the coefficients for the convergence of a double trigonometric series in the $L^p$-metric, where $0<p<1$. The results and their proofs have been motivated by the recent papers of A. S. Belov (2008) and F. Moricz (2010). Our basic tools in the proofs are the Hardy-Littlewood inequality for functions in $H^p$ and the Bernstein-Zygmund inequalities for the derivatives of trigonometric polynomials and their conjugates in the $L^p$-metric, where $0<p<1$.

Keywords: trigonometric series; Hardy-Littlewood inequality for functions in $H^p$; Bernstein-Zygmund inequalities for the derivative of trigonometric polynomials in $L^p$-metric for $0<p<1$; necessary conditions for the convergence in $L^p$-metric

Classification (MSC 2010): 42A16, 42A20, 42B05, 42B30, 42B99


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