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Mat. Zametki, 2025 Volume 117, Issue 2, Pages 315–327 (Mi mzm13482)

Estimation of the norm of the Hermite–Fejér interpolation operator with variable order derivatives in Sobolev spaces

A. I. Fedotov

Kazan (Volga Region) Federal University

Abstract: A new definition of the derivative of variable order is given based on the interpolation of derivatives of natural order. For the joint interpolation of a function and its derivative of variable order, interpolation operators of Hermite–Fejér type are constructed in the one-dimensional and multidimensional cases. Upper bounds for the norms of these operators in the one-dimensional and multidimensional periodic Sobolev spaces are obtained. It is shown that, in the one-dimensional case, the norm of this operator is bounded. In the multidimensional case, the upper bound depends on the ratio of the number of nodes for each coordinate.

Keywords: derivatives of variable order, interpolation operator of Hermite–Fejér type.

UDC: 517.518.823

MSC: 65R20

Received: 08.12.2023
Revised: 24.03.2024

DOI: 10.4213/mzm13482


 English version:
Mathematical Notes, 2025, 117:2, 326–337

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© Steklov Math. Inst. of RAS, 2026