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Recolouring reflexive digraphs
Authors:Richard C Brewster  Jae-baek Lee  Mark Siggers
Institution:1. Department of Mathematics and Statistics, Thompson Rivers University, Kamloops, BC, Canada;2. College of Natural Sciences, Kyungpook National University, Daegu 702-701, South Korea
Abstract:Given digraphs G and H, the colouring graph Col(G,H) has as its vertices all homomorphism of G to H. There is an arc ?? between two homomorphisms if they differ on exactly one vertex v, and if v has a loop we also require ?(v)?(v). The recolouring problem asks if there is a path in Col(G,H) between given homomorphisms ? and ψ. We examine this problem in the case where G is a digraph and H is a reflexive, digraph cycle.We show that for a reflexive digraph cycle H and a reflexive digraph G, the problem of determining whether there is a path between two maps in Col(G,H) can be solved in time polynomial in G. When G is not reflexive, we show the same except for certain digraph 4-cycles H.
Keywords:Homomorphisms  Recolouring  Reflexive digraphs  Hom-graph
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