# Vestnik КRAUNC. Fiz.-Mat. Nauki. 2023. vol. 42. no. 1. P. 9-26. ISSN 2079-6641

MATHEMATICS
https://doi.org/10.26117/2079-6641-2023-42-1-9-26
Research Article
Full text in Russian
MSC 35K35

Contents of this issue

Solvability of a Nonlocal Inverse Problem for a Fourth-Order Equation

A. B. Bekiev^*

Karakalpak State University named after Berdakh, Uzbekistan, Republic of Karakalpakstan, 230112, Nukus, Ch. Abdirov St. 1.

Abstract. In this paper, we consider a nonlocal inverse problem of finding an unknown right-hand side with
one variable for a fourth-order partial differential equation in a rectangular domain. The eigenfunctions and
associated functions of the corresponding spectral problem and its biorthogonal functions are complete and
form a Riesz basis in the space L_2\left(0,1\right) . Criteria for the uniqueness and existence of a solution to the considered nonlocal inverse problem for a fourth-order equation are established. The uniqueness of the solution of the nonlocal inverse problem follows from the completeness of the system of biorthogonal functions. The solution of the problem is constructed as the sum of a series in terms of eigenfunctions and associated functions of the corresponding spectral problem. Sufficient conditions are established for the boundary functions that guarantee existence and stability theorems for the solution of the problem under consideration. In a closed domain, absolute and uniform convergence of the found solution of the inverse problem is shown in the form of a series, as well as series obtained by term-by-term differentiation with respect to t and x two and four times, respectively, depending on the smoothness of the function given the initial conditions. In this case, small denominators arise, which hinder the convergence of these series. It is proved that, depending on the size of the domain, the set of non-zero solutions of the expression in the denominator is not empty. And also, it is shown that if this denominator is equal to zero, then this problem will have a non-trivial solution under homogeneous conditions. It is also proved that the solution of the inverse problem is stable in the norms of the spaces L_2, W^n_2 and C\left(\Omega\pm\right) with respect to changes in the input data.

Key words: fourth order equation, inverse nonlocal problem, uniqueness, existence, stability.

Received: 02.01.2023; Revised: 01.02.2023; Accepted: 08.04.2023; First online: 15.04.2023

For citation. Bekiev A. B. Solvability of a nonlocal inverse problem for a fourth-order equation. Vestnik KRAUNC. Fiz.-mat. nauki. 2023, 42: 1, 9-26. EDN: BJBNHI. https://doi.org/10.26117/2079-6641-2023-42-1-9-26.

Funding. The study was carried out without financial support from foundations.

Competing interests. There are no conflicts of interest regarding authorship and publication.

Contribution and Responsibility.  The author participated in the writing of the article and is fully responsible for submitting the final version of the article to print.

^* Correspondence: E-mail: ashir1976@mail.ru

The content is published under the terms of the Creative Commons Attribution 4.0 International License

© Institute of Cosmophysical Research and Radio Wave Propagation, 2023 (original layout, design, compilation)

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