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Forbidden subgraph colorings and the oriented chromatic number
, C.R. Subramanian
Published in
2009
Volume: 5874 LNCS
   
Pages: 60 - 71
Abstract
We present an improved upper bound of O(d1+ 1/m-1) for the (2,F)-subgraph chromatic number X2,F(G) of any graph G of maximum degree d. Here, m denotes the minimum number of edges in any member of F. This bound is tight up to a (log d)1/(m-1) multiplicative factor and improves the previous bound presented in [1]. We also obtain a relationship connecting the oriented chromatic number Xo(G) of graphs and the (j,F)-subgraph chromatic numbers Xj,F(G) introduced and studied in [1]. In particular, we relate oriented chromatic number and the (2, r)-treewidth chromatic number and show that Xo(G) ≤ k ((r + 1)2r)k-1 for any graph G having (2, r)-treewidth chromatic number at most k. The latter parameter is the least number of colors in any proper vertex coloring which is such that the subgraph induced by the union of any two color classes has treewidth at most r.We also generalize a result of Alon, et. al. [2] on acyclic chromatic number of graphs on surfaces to (2,F)-subgraph chromatic numbers and prove that X2,F(G) = O(γm/(2m-1)) for some constant m depending onlyon F. We also show that this bound is nearly tight. We then use this result to show that graphs of genus g have oriented chromatic number at most 2 O(g1/2+ε) for every fixed ε > 0. This improves the previously known bound of 2O(g4/7). We also refine the proof of a bound on Xo(G) obtained by Kostochka, et. al. in [3] to obtain an improved bound on Xo(G). © Springer-Verlag Berlin Heidelberg 2009.
About the journal
JournalLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
ISSN03029743