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JOURNALS // Vestnik of Saint Petersburg University. Mathematics. Mechanics. Astronomy // Archive

Vestnik of Saint Petersburg University. Mathematics. Mechanics. Astronomy, 2025 Volume 12, Issue 1, Pages 64–75 (Mi vspua340)

MATHEMATICS

The growth of subharmonic functions in a semicircle

A. A. Naumova

Kursk State University, 33, ul. Radishcheva, Kursk, 305000, Russian Federation

Abstract: Subharmonic functions $v$ in an unbounded open semiring, the growth of which is determined by the positive, continuous, increasing and unbounded function $\gamma(r)$, defined on $[0;\infty)$ (the growth function) are considered in the paper. Space of subharmonic functions of finite $\gamma$-type are denoted as $S(R, \gamma)$. In terms of Fourier coefficients, the criterion for belonging of a subharmonic function to the space $S(R, \gamma)$ is obtained. The paper contains some of the results by A.A. Kondratyuk, K.G. Malyutina, B.N. Khabibullina et al. extended to the functions defined in unbounded semiring. Transition to an unbounded semiring causes certain difficulties associated with complex behavior functions in a neighborhood of the boundary. Difference from the plane case appears already when receiving the criteria for belonging of subharmonic function to a given class.

Keywords: asymptotic stability, small periodic perturbation, oscillator.

UDC: 517.53

MSC: 31A20

Received: 09.05.2024
Revised: 26.06.2024
Accepted: 29.08.2024

DOI: 10.21638/spbu01.2025.105



© Steklov Math. Inst. of RAS, 2025