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Contributed Talks of RANDOM

Threshold Functions for Asymmetric Ramsey Properties Involving Cliques

Martin MarciniszynContact Information, Jozef SkokanContact Information, Reto SpöhelContact Information and Angelika StegerContact Information

(1)  Institute of Theoretical Computer Science, ETH Zurich, 8092 Zurich, Switzerland
(2)  Instituto de Matemática e Estatística, Universidade de São Paulo, 05508-090 São Paulo, SP, Brazil
Abstract
Consider the following problem: For given graphs G and F1,..., Fk, find a coloring of the edges of G with k colors such that G does not contain Fi in color i. For example, if every Fi is the path P3 on 3 vertices, then we are looking for a proper k-edge-coloring of G, i.e., a coloring of the edges of G with no pair of edges of the same color incident to the same vertex.
Rödl and Ruciński studied this problem for the random graph Gn,p in the symmetric case when k is fixed and F1=...=Fk=F. They proved that such a coloring exists asymptotically almost surely (a.a.s.) provided that pbnβ for some constants b=b(F,k) and β=β(F). Their proof was, however, non-constructive. This result is essentially best possible because for pBnβ, where B=B(F, k) is a large constant, such an edge-coloring does not exist. For this reason we refer to nβ as a threshold function.
In this paper we address the case when F1,..., Fk are cliques of different sizes and propose an algorithm that a.a.s. finds a valid k-edge-coloring of Gn,p with pbnβ for some constants b=b(F1,..., Fk, k) and β=β(F1,..., Fk). Kohayakawa and Kreuter conjectured that $n^{-\beta(F_1,\dots, F_k)}$ is a threshold function in this case. This algorithm can be also adjusted to produce a valid k-coloring in the symmetric case.

Contact Information Martin Marciniszyn
Email: mmarcini@inf.ethz.ch

Contact Information Jozef Skokan
Email: jozef@member.ams.org

Contact Information Reto Spöhel
Email: rspoehel@inf.ethz.ch

Contact Information Angelika Steger
Email: steger@inf.ethz.ch
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