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On the boundedness of general partial sums

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Abstract

From S. Banach’s results it follows that even for the function \(f(x)=1\) \((x\in [0,1])\) the general partial sums of its general Fourier series are not bounded a.e. on [0, 1]. In the present paper, we find conditions for the functions \(\varphi _n\) of an orthonormal system \((\varphi _n\)) under which the partial sums of functions from some differentiable class are bounded. We prove that the obtained results are best possible. We also investigate the properties of subsequences of general orthonormal systems.

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Authors and Affiliations

  1. Faculty of Exact and Natural Sciences, I. Javakhishvili Tbilisi State University, 13 University Str., 0186, Tbilisi, Georgia

    Vakhtang Tsagareishvili

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  1. Vakhtang Tsagareishvili
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Correspondence to Vakhtang Tsagareishvili.

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Tsagareishvili, V. On the boundedness of general partial sums. Period Math Hung 88, 429–442 (2024). https://doi.org/10.1007/s10998-023-00565-y

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