On the chromatic number of a random 5-regular graph

  • Authors:

  • J. Díaz;A. C. Kaporis;G. D. Kemkes;L. M. Kirousis;X. Pérez;N. Wormald

  • Affiliations:

  • Departament De Llenguatges I Sistemes Informàtics, universitat Politècnica De Catalunya, Campus Nord — ED. Omega 240, Jordi Girona Salgado, 1—3, E-08034 Barcelona, Catalunya;Department of Computer Engineering and Informatics, university of Patras, GR-265 04 Patras, Greece;Department of Combinatorics and Optimization, University of Waterloo, Waterloo, ON, N2L3G1 Canada;Department of Computer Engineering and Informatics, university of Patras, GR-265 04 Patras, Greece and Research Academic Computer Technology Institute, P.O. Box 1122, GR-261 10 Patras ...;Departament De Llenguatges I Sistemes Informàtics, universitat Politècnica De Catalunya, Campus Nord — ED. Omega 240, Jordi Girona Salgado, 1—3, E-08034 Barcelona, Catalunya;Department of Combinatorics and Optimization, University of Waterloo, Waterloo, ON, N2L3G1 Canada

  • Venue:
  • Journal of Graph Theory
  • Year:
  • 2009

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Abstract

It was only recently shown by Shi and Wormald, using the differential equation method to analyze an appropriate algorithm, that a random 5-regular graph asymptotically almost surely has chromatic number at most 4. Here, we show that the chromatic number of a random 5-regular graph is asymptotically almost surely equal to 3, provided a certain four-variable function has a unique maximum at a given point in a bounded domain. We also describe extensive numerical evidence that strongly suggests that the latter condition holds. The proof applies the small subgraph conditioning method to the number of locally rainbow balanced 3-colorings, where a coloring is balanced if the number of vertices of each color is equal, and locally rainbow if every vertex is adjacent to at least one vertex of each of the other colors. © 2009 Wiley Periodicals, Inc. J Graph Theory 61: 157–191, 2009