This paper deals with the problem of scheduling n tasks on m identical processors in the presence of communication delays. A new approach of modelisation by a decision graph and a resolution by a tabu search method is proposed. Initial solutions are constructed by list algorithms, and then improved by a tabu algorithm operating in two phases. The experiments carried on arbitrary graphs show the efficiency of our method and that it outperformed the principle existent heuristics.

Sequential scoring rules are multi-stage social choice tules that work as follows: at each stage of the process, a scoreis computed for each alternative by taking into account its position in the individual preference rankings, and thealternative with the lowest score is eliminated. The current paper studies the ability of these rules for choosing theCondorcet winner (or the strong Condorcet winner) when individual preferences are single-peaked.

We focus on performance study of routers in high-speednetwork through a queuing network analytical model. Such a model givesaccurate results about classical performance criteria. For example,analytical study of packet loss probabilities in a router uses aproduct-form queuing network. The analytical results are compared tosimulation results, and they provide routers managers with invaluableinformation for internal memories tuning.

In this paper, a model of the load transfer on a fullyconnected net is presented. Each processor can accept at most K tasks.A load difference of two tasks between two processors is a prohibitedsituation and when it may appear, an immediat and instantaneous transferis decided.The performances of the system are evaluated by the following indices:the reject probability, the throughput, the mean response time, thestationary probability distribution for a processor to host i tasks.The aim of this study is to evaluate the load transfer inpact thanks tothe comparison between the values of the indices without transfer andwith transfer. In particular the asymptotic behaviour for massivelyparallel systems is studied and interpreted. Calculated with an idealsituation, these comparisons yield upper bounds on the benefits that canbe expected from a transferring policy. Beyonds, the opportunity of thetransfer according to the values of the parameters can be studied. Themean number of transfers executed within a time unit and the mean numberof transfers of a given task are calculated. At last values of theindices when the number of accepted tasks K grows to infinity isstudied.

The main purpose of this paper is to give a method forconstruction of the reduced reachability graph for Stochastic Petri Nets(SPN), the symbolic graph. This construction is achieved by exploitingthe structural symetries in the net using the theory of bisimulation ofplaces for detecting isomorphic parts in the net. The symbolic graph,being isomorphic to an agregated Markov chain, may be used to provequalitative properties as liveness, boundness, ... Moreover, thisreduced graph make more easy the computation of the performance measuresof interest as the mean number of tokens in a place, the mean number offiring transition ... We have so developped a tool, SSPN (StochasticSymetric Petri nets), for generating the symbolic graph and deducingqualitatives and quantitatives properties.

A cooperative game is defined as a set of players and a cost function. The distribution of the whole cost between theplayers can be done using the core concept, that is the set of all undominated cost allocations which prevent playersfrom grouping. In this paper we study a game whose cost function comes from the optimal solution of a linear integercovering problem. We give necessary and sufficient conditions for the core to be nonempty and characterize itsallocations using linear programming duality. We also discuss a special allocation, called the nucleolus. Wecharacterize that allocation and show that it can be computed in polynomial time using a column generation method.