Complexity of Clausal Constraints Over Chains

  • Authors:
  • Nadia Creignou;Miki Hermann;Andrei Krokhin;Gernot Salzer

  • Affiliations:
  • Univ. de la Méditerranée, LIF (CNRS, UMR 6166), 13288, Marseille cedex 9, France;École Polytechnique, LIX (CNRS, UMR 7161), 91128, Palaiseau cedex, France;University of Durham, Department of Computer Science, DH1 3LE, Durham, UK;Technische Universität Wien, Favoritenstraße 9-11, 1040, Vienna, Austria

  • Venue:
  • Theory of Computing Systems
  • Year:
  • 2008

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Abstract

We investigate the complexity of the satisfiability problem of constraints over finite totally ordered domains. In our context, a clausal constraint is a disjunction of inequalities of the form x≥d and x≤d. We classify the complexity of constraints based on clausal patterns. A pattern abstracts away from variables and contains only information about the domain elements and the type of inequalities occurring in a constraint. Every finite set of patterns gives rise to a (clausal) constraint satisfaction problem in which all constraints in instances must have an allowed pattern. We prove that every such problem is either polynomially decidable or NP-complete, and give a polynomial-time algorithm for recognizing the tractable cases. Some of these tractable cases are new and have not been previously identified in the literature.