Three new upper bounds on the chromatic number

This paper introduces three new upper bounds on the chromatic number, without making any assumptions on the graph structure. The first one xi, is based on the number of edges and nodes, and is to be applied to any connected component of the graph, whereas zeta and eta are based on the degree of the nodes in the graph. The computation complexity of the three-bound computation is assessed. Theoretical and computational comparisons are also made with five well-known bounds from the literature, which demonstrate the superiority of the new upper bounds. (C) 2011 Elsevier B.V. All rights reserved.