Effect of Averaging Operators in Fuzzy Optimization of Reservoir Operation

Fuzzy multiobjective decision makingmodels generally rely on the aggregation of theobjectives to form a decision function. The generalizedaveraging operator is usually adopted for aggregatingmultiple and unequal objectives because it allows trade-off amongst the objectives, and has been shown to besuitable to model human decision making behavior. In thefield of water resource management, most of the decision-making problems involving the generalized averagingoperator implicitly assume the decision maker (DM) israther optimistic. The analysis of the DM's behaviorduring the aggregation process and its impact on theperformance of the system, has therefore never beenaddressed by many researchers and decision makers. Theaim of this paper is to investigate the relationshipbetween decision makers' index of optimism and the long-term performance of a reservoir resource. Morespecifically, the generalized averaging operator, whoseparameter can be interpreted as the DM's index ofoptimism, is imbedded into a fuzzy stochastic dynamicprogram (FSDP). This approach is developed andimplemented to derive optimal operating policies for thehydroelectric complex of the Uruguay River basin inSouthern Brazil. FSDP-derived policies with differentindices of optimism are then compared with simulation. Weshow that system performance may be influenced by thedecision maker's behavior during the aggregation, andthat the optimistic assumption may not yield tosatisfactory results, especially during critical timeperiods.     

Jobshop scheduling with imprecise durations: a fuzzy approach

Jobshop scheduling problems are NP-hard problems. The durations in the reality of manufacturing are often imprecise and the imprecision in data is very critical for the scheduling procedures. Therefore, the fuzzy approach, in the framework of the Dempster-Shafer theory, commands attention. The fuzzy numbers are considered as sets of possible probabilistic distributions. After a review of some issues concerning fuzzy numbers, we discuss the determination of a unique optimal solution of the problem and then we cast a meta-heuristic (simulated annealing-SA) to this particular framework for optimization. It should be stressed that the obtained schedule remains feasible for all realizations of the operations durations