Convergence theorems for graph sequences

TL;DR

This paper investigates the convergence behavior of Banach space-valued functions defined on finite graphs with bounded degrees, extending classical results to graph sequences with hyperfinite structures and applications to spectral theory.

Contribution

It extends convergence theorems and Fekete's Lemma to graph sequences with hyperfinite structures, linking them to spectral approximation and Banach space mappings.

Findings

Proves convergence of Banach space-valued functions on hyperfinite graph sequences.

Extends Fekete's Lemma to the setting of graph sequences and semigroups.

Demonstrates uniform approximation of the integrated density of states.

Abstract

In this paper, we deal with a notion of Banach space-valued mappings defined on a set consisting of finite graphs with uniformly bounded vertex degree. These functions will be endowed with certain boundedness and additivity criteria. We examine their normalized long-term behaviour along a particular class of graph sequences. Using techniques developed by Elek, we show convergence in the topology of the Banach space if the corresponding graph sequence possesses a hyperfinite structure. These considerations extend and complement the corresponding results for amenable groups. As an application, we verify the uniform approximation of the integrated density of states for bounded, finite range operators on discrete structures. Further, we extend results concerning an abstract version of Fekete's Lemma for amenable groups and cancellative semigroups to the geometric situation of convergent graph sequences.