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JOURNALS // Doklady Rossijskoj Akademii Nauk. Mathematika, Informatika, Processy Upravlenia // Archive

Dokl. RAN. Math. Inf. Proc. Upr., 2025 Volume 521, Pages 28–31 (Mi danma616)

MATHEMATICS

Notes on the recurrence of the Birkhoff sums

N. V. Denisova

Lomonosov Moscow State University

Abstract: The measure-preserving, but not necessarily invertible, ergodic transformations of the compact metric space with the Caratheodory measure are considered. The behavior of the Birkhoff sums for integrable and almost everywhere bounded functions with zero mean value in terms of the Caratheodory measure is studied. It is shown that for almost all points of the metric space there is an infinite sequence of “moments of time”; along which the Birkhoff sums tend to zero and at the same moments the trajectory points approach their initial position as close as possible (as in the Poincare return theorem). As an example, we consider the transformation $x\mapsto 2x$ mod 1; of the single segment 0 $\le x \le 1$ closely related to Bernoulli tests.

Keywords: metric space, Caratheodory measure, ergodic transformations, Birkhoff sums, recurrence properties, Hopf’s theorem, Bernoulli tests.

UDC: 511.9

Presented: V. V. Kozlov
Received: 02.01.2025
Revised: 04.02.2025
Accepted: 04.02.2025

DOI: 10.31857/S2686954325010046


 English version:
Doklady Mathematics, 2025, 111:2, 144–146

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© Steklov Math. Inst. of RAS, 2026