Section: New Results

Optimization

Participants : Salvador Abreu, Alejandro Reyes Amaro, Yves Caniou, Philippe Codognet, Daniel Diaz, Jean-Guillaume Fages, Xavier Lorca, Éric Monfroy, Florian Richoux, Louis-Martin Rousseau.

• The traveling salesman problem (TSP) is a challenging optimization problem for CP and OR that has many industrial applications. Its generalization to the degree constrained minimum spanning tree problem (DCMSTP) is being intensively studied by the OR community. In particular, classical solution techniques for the TSP are being progressively generalized to the DCMSTP. Recent work on cost-based relaxations has improved CP models for the TSP. However, CP search strategies have not yet been widely investigated for these problems. The contributions of this research are twofold. We first introduce a natural generalization of the weighted cycle constraint (WCC) to the DCMSTP. We then provide an extensive empirical evaluation of various search strategies. In particular, we show that significant improvement can be achieved via our graph interpretation of the state-of-the-art Last Conflict heuristic. The work was published in the Constraints journal, see the salesman and the tree: the importance of search in CP .

• In the context of nature inspired metaheuristics and its combination with CP, some new work were conducted in the field of ant colony to solve the software project scheduling problem [19] , and in the field of the Manufacturing Cell Design Problem [29] .

• We implement new algorithmic methods for constraint problems on massively parallel machines. In [18] , we propose an extensive study of homogeneous multi-walk parallel scheme for meta-heuristics both with and without communication. The next step will be to look at heterogeneous portfolio approaches where different solvers are looking in parallel for a solution to a given problem.