On the Power of Color Refinement

Abstract

Color refinement is a classical technique used to show that two given graphs G and H are non-isomorphic; it is very efficient, although it does not succeed on all graphs. We call a graph G amenable to color refinement if the color-refinement procedure succeeds in distinguishing G from any non-isomorphic graph H. Babai, Erdős, and Selkow (1982) have shown that random graphs are amenable with high probability. We determine the exact range of applicability of color refinement by showing that amenable graphs are recognizable in time \(O((n+m)\log n)\), where n and m denote the number of vertices and the number of edges in the input graph.