English

A tower lower bound for the degree relaxation of the Regularity Lemma

Combinatorics 2024-10-16 v2

Abstract

It is well-known that if (A,B)(A,B) is an ε2\tfrac{\varepsilon}{2}-regular pair (in the sense of Szemer\'edi) then there exist sets AAA'\subset A and BBB'\subset B' with AεA|A'|\leq \varepsilon|A| and BεB|B'|\leq \varepsilon|B| so that the degrees of all vertices in AAA\setminus A' differ by at most εB\varepsilon|B| and the degrees of all vertices in BBB\setminus B' differ by at most εA\varepsilon|A|. We call such a property "ε\varepsilon-degularity". This leads to the notion of an "ε\varepsilon-degular" partition of a graph in the same way as the definition of ε\varepsilon-regular pairs leads to the notion of ε\varepsilon-regular partitions. We show that there exist graphs in which any ε\varepsilon-degular partition requires the number of clusters to be tower(Θ(ε1/3))\mathrm{tower}(\Theta(\varepsilon^{-1/3})). That is, even though degularity is a substantial relaxation of regularity, in general one cannot improve much on the bounds that come with Szemer\'edi's regularity lemma.

Keywords

Cite

@article{arxiv.2410.05023,
  title  = {A tower lower bound for the degree relaxation of the Regularity Lemma},
  author = {Frederik Garbe and Jan Hladký},
  journal= {arXiv preprint arXiv:2410.05023},
  year   = {2024}
}

Comments

13 pages, 1 figure