Same-Relation Constraints

The ALLDIFFERENT constraint was one of the first global constraints [17] and it enforces the conjunction of one binary constraint, the not-equal constraint, for every pair of variables. By looking at the set of all pairwise not-equal relations at the same time, AllDifferent offers greater filtering power. The natural question arises whether we can generally leverage the knowledge that sets of pairs of variables all share the same relation. This paper studies exactly this question. We study in particular special constraint graphs like cliques, complete bipartite graphs, and directed acyclic graphs, whereby we always assume that the same constraint is enforced on all edges in the graph. In particular, we study whether there exists a tractable GAC propagator for these global Same-Relation constraints and show that AllDifferent is a huge exception: most Same-Relation Constraints pose NP-hard filtering problems. We present algorithms, based on AC-4 and AC-6, for one family of Same-Relation ...

• Type: Conference
• Year: 2009
• Where: CP
• Authors: Christopher Jefferson, Karen E. Petrie, Meinolf Sellmann, Serdar Kadioglu, Stanislav Zivný
• Keywords: Associated Constraint Graphs, CP 2009, Particular Binary Constraint, Programming Languages, Special Constraint Graphs