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 ODi) 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.


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© Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  • Nicolas Beldiceanu
    • 1
  • Fabien Hermenier
    • 1
  • Xavier Lorca
    • 1
  • Thierry Petit
    • 1
  1. 1.Mines-Nantes, LINA UMR CNRS 6241NantesFrance

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