Mardi 19 Mai
Heure: 
12:30  13:30 
Lieu: 
Salle B107, bâtiment B, Université de Villetaneuse 
Résumé: 
Approximating the energy storage problem and other continuous dynamic programs 
Description: 
Giacomo Nannicini We study the problem of optimally managing a source of renewable energy connected to the power grid, a battery, and potentially a household or some other form of energy sink. This problem can be naturally cast as a dynamic program. We propose a model for this problem that subsumes other models in the literature, and we analyze its complexity, showing that in the deterministic setting the problem is solvable in polynomial time, but it becomes #Phard in the stochastic setting. A variant of the problem that is commonly encountered in practice (i.e. the one where selling energy to the power grid is not allowed) admits a Fully Polynomial Time Approximation Scheme (FPTAS) if the energy levels are discretized; but what about the more natural case where energy is considered a continuous variable? We show that in this case, the problem belongs to a class of convex continuous dynamic programs that admits neither a multiplicative nor an additive approximation. We then show that we can construct a novel type of approximation scheme, where additive and multiplicative approximation are required at the same time but both can be arbitrarily small. We discuss a preliminary computational evaluation of this new type of approximation scheme for continuous convex dynamic programs, showing its potential. 
Heure: 
14:00  17:00 
Lieu: 
Salle B107, bâtiment B, Université de Villetaneuse 
Résumé: 
Explicit forms and combinatorial content of Levy stable distributions 
Description: 
Katarzyna Górska 
Jeudi 21 Mai
Heure: 
14:30  15:30 
Lieu: 
Salle B107, bâtiment B, Université de Villetaneuse 
Résumé: 
Reachability Preservation Based Parameter Synthesis for Timed Automata 
Description: 
Étienne André The synthesis of timing parameters consists in deriving conditions on the timing constants of a concurrent system such that it meets its specification. Parametric timed automata are a powerful formalism for parameter synthesis, although most problems are undecidable. We first address here the following reachability preservation problem: given a reference parameter valuation and a (bad) control state, do there exist other parameter valuations that reach this control state iff the reference parameter valuation does? We show that this problem is undecidable, and introduce a procedure that outputs a possibly underapproximated answer. We then show that our procedure can efficiently replace the behavioral cartography to partition a bounded parameter subspace into good and bad subparts; furthermore, our procedure can even outperform the classical badstate driven parameter synthesis semialgorithm, especially when distributed on a cluster. 

