English

On characterizing the critical graphs for matching Ramsey numbers

Combinatorics 2020-10-22 v2 Discrete Mathematics

Abstract

Given simple graphs H1,H2,,HcH_{1},H_{2},\ldots,H_{c}, the Ramsey number r(H1,H2,,Hc)r(H_{1},H_{2},\ldots,H_{c}) is the smallest positive integer nn such that every edge-colored KnK_{n} with cc colors contains a subgraph in color ii isomorphic to HiH_{i} for some i{1,2,,c}i\in\{1,2,\ldots,c\}. The critical graphs for r(H1,H2,,Hc)r(H_1,H_2,\ldots,H_c) are edge-colored complete graphs on r(H1,H2,,Hc)1r(H_1,H_2,\ldots,H_c)-1 vertices with cc colors which contain no subgraphs in color ii isomorphic to HiH_{i} for any i{1,2,,c}i\in \{1,2,\ldots,c\}. For n1n2nc1n_1\geq n_2\geq \ldots\geq n_c\geq 1, Cockayne and Lorimer (The Ramsey number for stripes, {\it J.\ Austral.\ Math.\ Soc.} \textbf{19} (1975), 252--256.) showed that r(n1K2,n2K2,,ncK2)=n1+1+i=1c(ni1)r(n_{1}K_{2},n_{2}K_{2},\ldots,n_{c}K_{2})=n_{1}+1+ \sum\limits_{i=1}^c(n_{i}-1), in which niK2n_{i}K_{2} is a matching of size nin_{i}. Using the Gallai-Edmonds Theorem, we characterized all the critical graphs for r(n1K2,n2K2,,ncK2)r(n_{1}K_{2},n_{2}K_{2},\ldots,n_{c}K_{2}), implying a new proof for this Ramsey number.

Keywords

Cite

@article{arxiv.1905.08456,
  title  = {On characterizing the critical graphs for matching Ramsey numbers},
  author = {Chuandong Xu and Hongna Yang and Shenggui Zhang},
  journal= {arXiv preprint arXiv:1905.08456},
  year   = {2020}
}
R2 v1 2026-06-23T09:14:38.389Z