Detachments of Complete Graphs

  • Authors:
  • Keith Edwards

  • Affiliations:
  • Division of Applied Computing, University of Dundee, Dundee, DD1 4HN, UK (e-mail: kjedwards@dundee.ac.uk)

  • Venue:
  • Combinatorics, Probability and Computing
  • Year:
  • 2005

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Abstract

A detachment of a graph $G$ is formed by splitting each vertex into one or more subvertices, and sharing the incident edges arbitrarily among the subvertices. In this paper we consider the question of whether a graph $H$ is a detachment of some complete graph $K_n$. When $H$ is large and restricted to belong to certain classes of graphs, for example bounded degree planar triangle-free graphs, we obtain necessary and sufficient conditions which give a complete characterization.A harmonious colouring of a simple graph $G$ is a proper vertex colouring such that each pair of colours appears together on at most one edge. The harmonious chromatic number $h(G)$ is the least number of colours in such a colouring. The results on detachments of complete graphs give exact results on harmonious chromatic number for many classes of graphs, as well as algorithmic results.