R89 | |
Boosting Search With Variable Elimination
Javier Larrosa (javier@ics.uci.edu)
Abstract
Variable elimination is the basic step of Adaptive Consistency[4]. It transforms the problem into an equivalent one, having one less variable. Unfortunately, there are many classes of problems for which it is infeasible, due to its exponential space and time complexity. However, by restricting variable elimination so that only low arity constraints are processed and recorded, it can be effectively combined with search, because the elimination of variables, reduces the search tree size. In this paper we introduce VarElimSearch(S;k), a hybrid meta-algorithm that combines search and variable elimination. The parameter S names the particular search procedure and k controls the tradeoff between the two strategies. The algorithm is space exponential in k. Regarding time, we show that its complexity is bounded by k and a structural parameter from the constraint graph. We also provide experimental evidence that the hybrid algorithm can outperform stateoftheart algorithms in binary sparse problems. Experiments cover the tasks of finding one solution and the best solution (MaxCSP). Specially in the MaxCSP case, the advantage of our approach can be overwhelming. |