Evènement pour le groupe Modélisation et Verification

Date 2011-04-28  11:30-12:30
TitreA lazy reachability algorithm for timed automata 
RésuméWe consider the classic reachability problem for timed automata: given an automaton, decide if there exists a path from its initial state to a given target state. The standard solution to this problem involves computing the *zone graph* of the automaton, which in principle could be infinite. In order to make the graph finite, zones are approximated using an extrapolation operator. For reasons of efficiency it is required that an extrapolation of a zone is always a zone; and in particular that it is *convex*. We propose a new solution to the reachability problem that uses no such extrapolation operators. To ensure termination, we provide an efficient algorithm to check if a zone is included in the *region closure* of another. Although theoretically better, closure cannot be used in the standard algorithm since a closure of a zone may not be convex. The structure of this new algorithm permits to calculate approximating parameters on-the-fly during exploration of the zone graph, as opposed to the current methods which do it by a static analysis of the automaton prior to the exploration. This allows for further improvements in the algorithm. Promising experimental results are presented. Joint work with Frédéric Herbreteau, Dileep Kini, Igor Walukiewicz  
OrateurSrivathsan Balaguru 

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