CP '01 Proceedings of the 7th International Conference on Principles and Practice of Constraint Programming
Global Constraints for Lexicographic Orderings
CP '02 Proceedings of the 8th International Conference on Principles and Practice of Constraint Programming
Breaking Row and Column Symmetries in Matrix Models
CP '02 Proceedings of the 8th International Conference on Principles and Practice of Constraint Programming
Symmetry Breaking using Value Precedence
Proceedings of the 2006 conference on ECAI 2006: 17th European Conference on Artificial Intelligence August 29 -- September 1, 2006, Riva del Garda, Italy
An efficient way of breaking value symmetries
AAAI'06 Proceedings of the 21st national conference on Artificial intelligence - Volume 1
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Multi-aspect Assignment Problems (MAPs) can be naturally formulated into various matrix models of Constraint Satisfaction Problems (CSPs), which can contain both variable and value symmetries, using different viewpoints. While variable symmetry breaking constraints can be expressed relatively easily and executed efficiently by enforcing lexicographic ordering, value symmetry breaking constraints are difficult to formulate. We show when value symmetries in one viewpoint correspond to variable symmetries in another, and when symmetry breaking constraints in two viewpoints are consistent. Our results allow tackling value symmetries efficiently using additional viewpoints and channeling constraints. Experiments on the social golfer problem and a variant of the quasigroup existence problem confirm the benefits of our proposal against conventional methods.