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Conference Papers Year : 2010

The Increasing Nvalue Constraint


This paper introduces the Increasing_Nvalue constraint, which restricts the number of distinct values assigned to a sequence of variables so that each variable in the sequence is less than or equal to its successor. This constraint is a specialization of the Nvalue constraint, motivated by symmetry breaking. Propagating the Nvalue constraint is known as an NP-hard problem. However, we show that the chain of non strict inequalities on the variables makes the problem polynomial. We propose an algorithm achieving generalized arc-consistency in O(ΣDi) time, where ΣDi is the sum of domain sizes. This algorithm is an improvement of filtering algorithms obtained by the automaton-based or the Slide-based reformulations. We evaluate our constraint on a resource allocation problem.

Dates and versions

hal-00915800 , version 1 (09-12-2013)



Nicolas Beldiceanu, Fabien Hermenier, Xavier Lorca, Thierry Petit. The Increasing Nvalue Constraint. Integration of AI and OR Techniques in Constraint Programming for Combinatorial Optimization Problems, Jun 2010, Bologna, Italy. ⟨10.1007/978-3-642-13520-0_5⟩. ⟨hal-00915800⟩
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