The equivalence of precompactness, zero maximal pattern entropy and bounded mean complexity for finite partitions

TL;DR

This paper establishes the equivalence of several low-complexity notions for finite partitions in probability spaces and group actions, linking precompactness, entropy, mean complexity, and almost periodicity.

Contribution

It proves the equivalence of multiple low-complexity conditions for finite partitions in both probability spaces and group actions, unifying various concepts.

Findings

Precompactness in Rokhlin metric is equivalent to zero maximal pattern entropy.

Characteristic functions of atoms are precompact in L^2 if and only if the partition has zero maximal pattern entropy.

Zero maximal pattern entropy corresponds to mean equicontinuity and almost periodicity of characteristic functions.

Abstract

In this paper, we investigate several types of low complexity of finite partitions, including precompactness, zero maximal pattern entropy, bounded mean complexity and mean equicontinuity. We first show that a collection of finite partitions in a standard probability space is precompact in the Rokhlin metric if and only if it has zero maximal pattern entropy if and only if the collection of the characteristic functions of atoms in those partitions is precompact in $L^2$ if and only if it has bounded mean complexity with respect the Hamming distance. Next, we show that for a countably infinite discrete amenable group acting on a standard probability space, a finite partition has zero maximal pattern entropy if and only if each characteristic function of atom in the partition is almost periodic if and only if it has bounded mean complexity with respect to some (and hence any) F{\o}lner sequence if and only if it is mean equicontinuous with respect to some (and hence any) tempered F{\o}lner sequence.