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Frederic Koriche

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3 papers

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IJCAI Conference 2022 Conference Paper

Best Heuristic Identification for Constraint Satisfaction

Frederic Koriche
Christophe Lecoutre
Anastasia Paparrizou
Hugues Wattez

In constraint satisfaction problems, the variable ordering heuristic takes a central place by selecting the variables to branch on during backtrack search. As many hand-crafted branching heuristics have been proposed in the literature, a key issue is to identify, from a pool of candidate heuristics, which one is the best for solving a given constraint satisfaction task. Based on the observation that modern constraint solvers are using restart sequences, the best heuristic identification problem can be cast in the context of multi-armed bandits as a non-stochastic best arm identification problem. Namely, during each run of some given restart sequence, the bandit algorithm selects a branching heuristic and receives a reward for this heuristic before proceeding to the next run. The goal is to identify the best heuristic using few runs, and without any stochastic assumption about the constraint solver. In this study, we propose an adaptive variant of Successive Halving that exploits Luby's universal restart sequence. We analyze the convergence of this bandit algorithm in the non-stochastic setting, and we demonstrate its empirical effectiveness on various constraint satisfaction benchmarks.

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IJCAI Conference 2022 Conference Paper

On Preferred Abductive Explanations for Decision Trees and Random Forests

Gilles Audemard
Steve Bellart
Louenas Bounia
Frederic Koriche
Jean-Marie Lagniez
Pierre Marquis

Abductive explanations take a central place in eXplainable Artificial Intelligence (XAI) by clarifying with few features the way data instances are classified. However, instances may have exponentially many minimum-size abductive explanations, and this source of complexity holds even for ``intelligible'' classifiers, such as decision trees. When the number of such abductive explanations is huge, computing one of them, only, is often not informative enough. Especially, better explanations than the one that is derived may exist. As a way to circumvent this issue, we propose to leverage a model of the explainee, making precise her / his preferences about explanations, and to compute only preferred explanations. In this paper, several models are pointed out and discussed. For each model, we present and evaluate an algorithm for computing preferred majoritary reasons, where majoritary reasons are specific abductive explanations suited to random forests. We show that in practice the preferred majoritary reasons for an instance can be far less numerous than its majoritary reasons.

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AAAI Conference 2006 Conference Paper

Acquiring Constraint Networks Using a SAT-based Version Space Algorithm

Christian Bessiere
Frederic Koriche

Constraint programming is a commonly used technology for solving complex combinatorial problems. However, users of this technology need significant expertise in order to model their problems appropriately. We propose a basis for addressing this problem: a new SAT-based version space algorithm for acquiring constraint networks from examples of solutions and non-solutions of a target problem. An important advantage of the algorithm is the ease with which domain-specific knowledge can be exploited.

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