Local Search Methods for Learning Bayesian Networks Using a Modified Neighborhood in the Space of DAGs

The dominant approach for learning Bayesian networks from data is based on the use of a scoring metric, that evaluates the fitness of any given candidate network to the data, and a search procedure, that explores the space of possible solutions. The most efficient methods used in this context are (Iterated) Local Search algorithms. These methods use a predefined neighborhood structure that defines the feasible elementary modifications (local changes) that can be applied to a given solution in order to get another, potentially better solution. If the search space is the set of directed acyclic graphs (dags), the usual choices for local changes are arc addition, arc deletion and arc reversal. In this paper we propose a new definition of neighborhood in the dag space, which uses a modified operator for arc reversal. The motivation for this new operator is the observation that local search algorithms experience problems when some arcs are wrongly oriented. We exemplify the general usefulness of our proposal by means of a set of experiments with different metrics and different local search methods, including Hill-Climbing and Greedy Randomized Adaptive Search Procedure (GRASP), as well as using several domain problems.