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Abstract

The constraint NValue counts the number of different values assigned to a vector of variables. Propagating generalized arc consistency on this constraint is NP-hard. We show that computing even the lower bound on the number of values is NP-hard. We therefore study different approximation heuristics for this problem. We introduce three new methods for computing a lower bound on the number of values. The first two are based on the maximum independent set problem and are incomparable to a previous approach based on intervals. The last method is a linear relaxation of the problem. This gives a tighter lower bound than all other methods, but at a greater asymptotic cost.

Keywords

Constraint Satisfaction Problem Intersection Graph Interval Graph Maximal Match Linear Relaxation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Christian Bessiere
    • 1
  • Emmanuel Hebrard
    • 2
  • Brahim Hnich
    • 3
  • Zeynep Kiziltan
    • 4
  • Toby Walsh
    • 2
  1. 1.LIRMMCNRS/University of MontpellierFrance
  2. 2.NICTA and UNSWSydneyAustralia
  3. 3.4C and UCCCorkIreland
  4. 4.University of BolognaItaly

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