On the integration of singleton consistencies and look-ahead heuristics

Abstract

The efficiency of complete solvers depends both on constraint propagation to narrow the domains and some form of complete search. Whereas constraint propagators should achieve a good trade-off between their complexity and the pruning that is obtained, search heuristics take decisions based on information about the state of the problem being solved. In general, these two components are independent and are indeed considered separately. A recent family of algorithms have been proposed to achieve a strong form of consistency called Singleton Consistency (SC). These algorithms perform a limited amount of search and propagation (lookahead) to remove inconsistent values from the variables domains, making SC costly to maintain. This paper follows from the observation that search states being explored while enforcing SC are an important source of information about the future search space which is being ignored. In this paper we discuss the integration of this look-ahead information into variable and value selection heuristics, and show that significant speedups are obtained in a number of standard benchmark problems. © 2008 Springer Berlin Heidelberg.