Counting $r$-graphs without forbidden configurations
Abstract
One of the major problems in combinatorics is to determine the number of -uniform hypergraphs (-graphs) on vertices which are free of certain forbidden structures. This problem dates back to the work of Erd\H{o}s, Kleitman and Rothschild, who showed that the number of -free graphs on vertices is . Their work was later extended to forbidding graphs as induced subgraphs by Pr\"omel and Steger. Here, we consider one of the most basic counting problems for -graphs. Let be the -graph with vertices and edge. What is the number of induced -free -graphs on vertices? We show that the number of such -graphs is of order . More generally, we determine asymptotically the number of induced -free -graphs on vertices for all families of -graphs on vertices. We also provide upper bounds on the number of -graphs on vertices which do not induce edges on any set of vertices, where is a list which does not contain consecutive integers in its complement. Our bounds are best possible up to a constant multiplicative factor in the exponent when . The main tool behind our proof is counting the solutions of a constraint satisfaction problem.
Keywords
Cite
@article{arxiv.2107.14798,
title = {Counting $r$-graphs without forbidden configurations},
author = {József Balogh and Felix Christian Clemen and Letícia Mattos},
journal= {arXiv preprint arXiv:2107.14798},
year = {2021}
}
Comments
18 pages