Algebraic characterization of uniquely vertex colorable graphs

  • Authors:
  • Christopher J. Hillar;Troels Windfeldt

  • Affiliations:
  • Department of Mathematics, Texas A&M University, College Station, TX 77843, USA;Department of Mathematical Sciences, University of Copenhagen, Denmark

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2008

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Abstract

The study of graph vertex colorability from an algebraic perspective has introduced novel techniques and algorithms into the field. For instance, it is known that k-colorability of a graph G is equivalent to the condition 1@?I"G","k for a certain ideal I"G","k@?k[x"1,...,x"n]. In this paper, we extend this result by proving a general decomposition theorem for I"G","k. This theorem allows us to give an algebraic characterization of uniquely k-colorable graphs. Our results also give algorithms for testing unique colorability. As an application, we verify a counterexample to a conjecture of Xu concerning uniquely 3-colorable graphs without triangles.