Abstract

Exploiting Short Supports for Generalised Arc Consistency for Arbitrary Constraints
Exploiting Short Supports for Generalised Arc Consistency for Arbitrary Constraints
Peter Nightingale, Ian P. Gent, Christopher Jefferson, Ian Miguel
Special-purpose constraint propagation algorithms (such as those for the element constraint) frequently make implicit use of short supports — by examining a subset of the variables, they can infer support for all other variables and values and save substantial work. However, to date general purpose propagation algorithms (such as GAC-Schema) rely upon supports involving all variables. We demonstrate how to employ short supports in a new general purpose propagation algorithm called ShortGAC. This works when provided with either an explicit list of allowed short tuples, or a function to calculate the next supporting short tuple. Empirical analyses demonstrate the efficiency of ShortGAC compared to other general-purpose propagation algorithms. In some cases ShortGAC even exhibits similar performance to special-purpose propagators.