![]() |
Discrete Mathematics & Theoretical Computer Science |
We consider non-trivial homomorphisms to reflexive oriented graphs in which some pair of adjacent vertices have the same image. Using a notion of convexity for oriented graphs, we study those oriented graphs that do not admit such homomorphisms. We fully classify those oriented graphs with tree-width $2$ that do not admit such homomorphisms and show that it is NP-complete to decide if a graph admits an orientation that does not admit such homomorphisms. We prove analogous results for $2$-edge-coloured graphs. We apply our results on oriented graphs to provide a new tool in the study of chromatic number of orientations of planar graphs -- a long-standing open problem.
Source : ScholeXplorer
IsRelatedTo DOI 10.1016/j.dam.2009.09.017 Source : ScholeXplorer IsRelatedTo DOI 10.1016/j.endm.2008.01.007
|