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Graphs and Combinatorics

, Volume 32, Issue 5, pp 1707–1721 | Cite as

Decomposing Oriented Graphs into Six Locally Irregular Oriented Graphs

  • Julien Bensmail
  • Gabriel Renault
Original Paper

Abstract

An undirected graph G is locally irregular if every two of its adjacent vertices have distinct degrees. We say that G is decomposable into k locally irregular graphs if there exists a partition \(E_1 \cup E_2 \cup \cdots \cup E_k\) of the edge set E(G) such that each \(E_i\) induces a locally irregular graph. It was recently conjectured by Baudon et al. that every undirected graph admits a decomposition into at most three locally irregular graphs, except for a well-characterized set of indecomposable graphs. We herein consider an oriented version of this conjecture. Namely, can every oriented graph be decomposed into at most three locally irregular oriented graphs, i.e. whose adjacent vertices have distinct outdegrees? We start by supporting this conjecture by verifying it for several classes of oriented graphs. We then prove a weaker version of this conjecture. Namely, we prove that every oriented graph can be decomposed into at most six locally irregular oriented graphs. We finally prove that even if our conjecture were true, it would remain NP-complete to decide whether an oriented graph is decomposable into at most two locally irregular oriented graphs.

Keywords

Oriented graph Locally irregular oriented graph Decomposition into locally irregular graphs Complexity 

Notes

Acknowledgments

The authors thank the anonymous referees for their careful reading of a previous version of the current paper. J. Bensmail was supported by ERC Advanced Grant GRACOL, Project No. 320812.

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Copyright information

© Springer Japan 2016

Authors and Affiliations

  1. 1.Department of Applied Mathematics and Computer ScienceTechnical University of DenmarkLyngbyDenmark
  2. 2.University of Bordeaux, LaBRI, UMR 5800TalenceFrance
  3. 3.CNRS, LaBRI, UMR 5800TalenceFrance

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