LIP6, salle 24-25/405. Instructions pour venir ici.
Abstract : Decision Diagrams (DD) have been successfully used to store the state space of large discrete event dynamic systems (DEDS), typically described in terms of discrete variables and events. The availability of well-established libraries, as well as more recent ones, makes the use of DD in this context very straightforward. On the other side it is well known that the effectiveness of a DD representation of a state space is strongly dependent on the specific assignment of the DEDS variable to the DD levels, an NP-complete problem. Given that a brute force approach is not feasible, many heuristics have been defined. This talk concentrate on heuristics for variable orders, their definition and their evaluation. In particular I will concentrate on heuristics that make use of structural information of the system (like p-semiflows for Petri net), on metrics to evaluate such heuristics and on the use of metrics as meta-heuristics for the selection of "good" orders.
Abstract : SAT solvers are now widely used to solve a large variety of problems, including formal verification of systems. SAT problems derived from such applications often exhibit symmetry properties that could be exploited to speed up their solving. Static symmetry breaking is so far the most popular approach to take advantage of symmetries. It relies on a symmetry preprocessor which augments the initial problem with constraints that force the solver to consider only a few configurations among the many symmetric ones. In this talk, we present a way to exploit symmetries during the solver search.