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Conference Papers Year : 2005

Filtering Algorithms for the NValue Constraint

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.

Dates and versions

lirmm-00106098 , version 1 (13-10-2006)

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Christian Bessiere, Emmanuel Hébrard, Brahim Hnich, Zeynep Kiziltan, Toby Walsh. Filtering Algorithms for the NValue Constraint. CPAIOR, May 2005, Prague, Czech Republic. pp.79-93, ⟨10.1007/11493853_8⟩. ⟨lirmm-00106098⟩
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