A Mamma e Papà e ai miei fratelli
AbstractThe success of portfolio algorithms in competitions in the area of combinatorial problem solving, as well as in practice, has motivated interest in the development of new approaches to determine the best solver for the problem at hand. Yet, although there are a number of ways in which this decision can be made, it always relies on a rich set of features to identify and distinguish the structure of the problem instances.In this thesis, however, it is firstly shown how not all the features in the problem have the same relevancy. Then it is presented how one of the most successful portfolio approaches, ISAC, can be augmented by taking into account the past performance of solvers as part of the feature vector. Testing on a variety of SAT datasets, it is here proved how the new formulation continuously outperforms an unmodified/standard version of ISAC.This thesis presents a novel strategy that tackles the problem of algorithm portfolios applying machine learning techniques and improves a state-of-the-art portfolio algorithms approaches (ISAC).Starting from the basic assumptions behind the standard ISAC methodology that the given collection of features can be used to correctly identify the structure of each instance, an important step has been to be able to improve clustering, grouping together instances that prefer to be solved by the same solver. It has been created, and here is presented, a methodology to redefine the feature vector including past performance of the solvers. The final result is named SNNAP: Solver-based Nearest Neighbor for Algorithm Portfolios which is here presented.