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JOURNALS // Matematicheskie Zametki // Archive

Mat. Zametki, 1972 Volume 12, Issue 3, Pages 313–324 (Mi mzm9884)

This article is cited in 10 papers

Generalized variation, the Banach indicatrix, and the uniform convergence of Fourier series

K. I. Oskolkov

V. A. Steklov Mathematical Institute, Academy of Sciences of the USSR

Abstract: It is proved that if the continuous periodic function $f$ has bounded $\Phi$-variation, then the deviation of $f$ from the sum of $n$ terms of its Fourier series has the bound
$$ ||f-S_n(f)||\leqslant c\int_0^{\omega(\pi n^{-1})}\log(v_\Phi(f)/\Phi(\xi))d\xi. $$
Here $c$ is an absolute constant, $\omega$ is the modulus of continuity, $v_\Phi(f)$ is the complete $\Phi$-variation of $f$ over a period. It is established that the Salem and Garsia–Sawyer criteria for the uniform convergence of the Fourier series in terms of the $\Phi$-variation and the Banach indicatrix respectively are definitive, and it is proved that the second of these variants is a corrolary of the first.

UDC: 517.5

Received: 27.01.1972


 English version:
Mathematical Notes, 1972, 12:3, 619–625

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