Localiser des sources d'incohérence spécifiques sans les calculer toutes

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Une nouvelle méthode hybride pour calculer tous les MSS et tous les MUS

Dans ce papier, nous présentons une nouvelle technique complète permettant le calcul des sous-formules maximales consistantes (MSS) et des formules minimales inconsistantes (MUS) d'un ensemble de clauses booléennes. Cette approche améliore la meilleure technique complète connue de plusieurs manières. Elle utilise à la fois une recherche locale peu coûteuse en ressources et le nouveau concept de clause critique pour améliorer un algorithme complet proposé par Liffiton et Sakallah. Cette hybridation permet l'obtention de gains exponentiels. Ainsi, des résultats expérimentaux montrent que cette nouvelle approche dépasse la meilleure méthode proposée jusque ici

On Finding Minimally Unsatisfiable Cores of CSPs

International audienceWhen a Constraint Satisfaction Problem (CSP) admits no solution, it can be useful to pinpoint which constraints are actually contradicting one another and make the problem infeasible. In this paper, a recent heuristic-based approach to compute infeasible min- imal subparts of discrete CSPs, also called Minimally Unsatisfiable Cores (MUCs), is improved. The approach is based on the heuristic exploitation of the number of times each constraint has been falsified during previous failed search steps. It appears to en- hance the performance of the initial technique, which was the most efficient one until now

Extraction de sous-formules minimales inconsistantes

Une sous-formule minimale inconsistante (Minimally Unsatisfiable Subformula ou MUS en anglais) représente la plus petite cause d'incohérence d'une instance SAT en terme de nombre de clauses. Extraire un ou plusieurs MUS s'avère donc très utile, car ceux-ci circonscrivent les sources d'inconsistance d'une formule CNF. Dans ce papier, une nouvelle méta-heuristique permettant l'approximation ou le calcul d'un MUS est présentée. Une comparaison avec les méthodes les plus compétitives est effectuée, et montre que le plus souvent, en pratique, cette approche surpasse les résultats obtenus par les autres méthodes existantes

Using Local Search to Find \MSSes and MUSes

International audienceIn this paper, a new complete technique to compute Maximal Satisfiable Subsets (MSSes) and Minimally Unsatisfiable Subformulas (MUSes) of sets of Boolean clauses is introduced. The approach improves the currently most efficient complete technique in several ways. It makes use of the powerful concept of critical clause and of a computationally inexpensive local search oracle to boost an exhaustive algorithm proposed by Liffiton and Sakallah. These features can allow exponential efficiency gains to be obtained. Accordingly, experimental studies show that this new approach outperforms the best current existing exhaustive ones

Preserving Partial Solutions while Relaxing Constraint Networks

International audienceThis paper is about transforming constraint net- works to accommodate additional constraints in specific ways. The focus is on two intertwined issues. First, we investigate how partial solutions to an initial network can be preserved from the potential impact of additional constraints. Second, we study how more permissive constraints, which are intended to enlarge the set of solutions, can be accommodated in a constraint network. These two problems are studied in the general case and the light is shed on their relationship. A case study is then investigated where a more permissive additional constraint is taken into account through a form of network relaxation, while some previous partial solutions are preserved at the same time

Integrating Conflict Driven Clause Learning to Local Search

This article introduces SatHyS (SAT HYbrid Solver), a novel hybrid approach for propositional satisfiability. It combines local search and conflict driven clause learning (CDCL) scheme. Each time the local search part reaches a local minimum, the CDCL is launched. For SAT problems it behaves like a tabu list, whereas for UNSAT ones, the CDCL part tries to focus on minimum unsatisfiable sub-formula (MUS). Experimental results show good performances on many classes of SAT instances from the last SAT competitions

A CSP solver focusing on FAC variables

International audienceThe contribution of this paper is twofold. On the one hand, it introduces a concept of FAC variables in discrete Constraint Satisfaction Prob- lems (CSPs). FAC variables can be discovered by local search techniques and powerfully exploited by MAC-based methods. On the other hand, a novel syn- ergetic combination schema between local search paradigms, generalized arc- consistency and MAC-based algorithms is presented. By orchestrating a multiple- way flow of information between these various fully integrated search compo- nents, it often proves more competitive than the usual techniques on most classes of instances

Relax!

International audienceThis paper is concerned with a form of relaxation of constraint networks. The focus is on situations where additional constraints are intended to extend a non- empty set of preexisting solutions. These constraints require a speci c treatment since merely inserting them inside the network would lead to their preemption by more restrictive ones. Several approaches to handle these additional constraints are investigated from con- ceptual and experimental points of view