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On the Size-Ramsey Number of Cycles

Published online by Cambridge University Press:  17 July 2019

R. Javadi*
Affiliation:
Department of Mathematical Sciences, Isfahan University of Technology, Isfahan, 84156-83111, Iran. Emails: rjavadi@cc.iut.ac.ir, f.khoeini@math.iut.ac.ir, romidi@cc.iut.ac.ir
F. Khoeini
Affiliation:
Department of Mathematical Sciences, Isfahan University of Technology, Isfahan, 84156-83111, Iran. Emails: rjavadi@cc.iut.ac.ir, f.khoeini@math.iut.ac.ir, romidi@cc.iut.ac.ir
G. R. Omidi
Affiliation:
Department of Mathematical Sciences, Isfahan University of Technology, Isfahan, 84156-83111, Iran. Emails: rjavadi@cc.iut.ac.ir, f.khoeini@math.iut.ac.ir, romidi@cc.iut.ac.ir School of Mathematics, Institute for Research in Fundamental Sciences(IPM), PO box 19395-5746, Tehran, Iran
A. Pokrovskiy
Affiliation:
Department of Economics, Mathematics, and Statistics, Birkbeck, University of London, London WC1E 7HX, UK. Email: dr.alexey.pokrovskiy@gmail.com
*
*Corresponding author. Email: rjavadi@cc.iut.ac.ir

Abstract

For given graphs G1,…, Gk, the size-Ramsey number $\hat R({G_1}, \ldots ,{G_k})$ is the smallest integer m for which there exists a graph H on m edges such that in every k-edge colouring of H with colours 1,…,k, H contains a monochromatic copy of Gi of colour i for some 1 ≤ ik. We denote $\hat R({G_1}, \ldots ,{G_k})$ by ${\hat R_k}(G)$ when G1 = ⋯ = Gk = G.

Haxell, Kohayakawa and Łuczak showed that the size-Ramsey number of a cycle Cn is linear in n, ${\hat R_k}({C_n}) \le {c_k}n$ for some constant ck. Their proof, however, is based on Szemerédi’s regularity lemma so no specific constant ck is known.

In this paper, we give various upper bounds for the size-Ramsey numbers of cycles. We provide an alternative proof of ${\hat R_k}({C_n}) \le {c_k}n$ , avoiding use of the regularity lemma, where ck is exponential and doubly exponential in k, when n is even and odd, respectively. In particular, we show that for sufficiently large n we have ${\hat R_2}({C_n}) \le {10^5} \times cn$ , where c = 6.5 if n is even and c = 1989 otherwise.

Type
Paper
Copyright
© Cambridge University Press 2019 

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Footnotes

Research partially supported by INSF grant no. 95844679.

Research partially carried out in the IPM-Isfahan Branch and in part supported by a grant from IPM (no. 95050217).

§

Research partially supported by SNSF grant 200021-149111.

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