The complexity of arc-colorings for directed hypergraphs

  • Authors:
  • Andrea Vietri

  • Affiliations:
  • Dipartimento Metodi e Modelli Matematici, Università La Sapienza, Via A. Scarpa, 16, 00161 Rome, Italy

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2004

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Abstract

We address some complexity questions related to the arc-coloring of directed hypergraphs. Such hypergraphs arise as a generalization of digraphs, by allowing the tail of each arc to consist of more than one node. The related arc-coloring extends the notion of digraph arc-coloring, which has been studied by diverse authors. Using two classical results we easily prove that the optimal coloring of a digraph, as well as the 2-coloring test for every directed hypergraph, require polynomial time. Instead, the k-colorability problem for some fixed degree d is shown to be NP-complete if k ≥ d ≥ 2 and k ≥ 3, even if the input is restricted to the so-called non-overlapping hypergraphs. We also describe a subclass of hypergraphs for which the 3-colorability test is polynomially decidable. Some results are rephrased and proved using suitable adjacency matrices, namely walls.