FacilitylocationmodelsfordistributionsystemdesignThedesignofthedistributionsystemisastrategicissueforalmosteverycompany.Theproblemoflocatingfacilitiesandallocatingcustomerscoversthecoretopicsofdistributionsystemdesign.Industrialfirmsmustlocatefabrication(制造厂)andassemblyplants(组装厂)aswellaswarehouses(仓库).Storeshavetobelocatedbyretailoutlets(零售网点).Theabilitytomanufactureandmarketitsproductsisdependentinpartonthelocationofthefacilities.Similarly,governmentagencieshavetodecideaboutthelocationofoffices,schools,hospitals,firestations,etc.Ineverycase,thequalityoftheservicesdependsonthelocationofthefacilitiesinrelationtootherfacilities.TypesofmodelsFacilitylocationmodelscanbebroadlyclassifiedasfollows:Modelswithoutcapacityconstraintsdonotrestrict(限制)demandallocation.Ifcapacityconstraintsforthepotentialsiteshavetobeobeyeddemandhastobeallocatedcarefully.Inthelattercasewehavetoexaminewhethersingle-sourcing(单来源)ormultiple-sourcing(多来源)isessential.Single-stagemodels(单阶段模型)focusondistributionsystemscoveringonlyonestageexplicitly.Inmulti-stagemodels(多阶段模型)theflowofgoodscomprisingseveralhierarchical(层次)stageshastobeexamined.Single-productmodels(单产品模型)arecharacterizedbythefactthatdemand,costandcapacityforseveralproductscanbeaggregatedtoasinglehomogeneousproduct.Ifproductsareinhomogeneoustheireffectonthedesignofthedistributionsystemhastobeanalyzed,viz.multi-productmodels(多产品模型)havetobestudied.Locationmodelsbaseontheassumptionthatdemandisinelastic(无弹性的),thatis,demandisindependentofspatialdecisions.Ifdemandiselastic(弹性的)therelationshipbetween,e.g.,distanceanddemandhastobetakenintoaccountexplicitly.Inthelattercasecostminimization(成本最小)hastobereplacedthrough,forexample,revenuemaximization(收益最大).Staticmodels(静态模型)trytooptimizesystemperformance(性能)foronerepresentative(代表)period.Bycontrastdynamicmodels(动态模型)reflectdata(cost,demand,capacities,etc.)varyingovertimewithinagivenplanninghorizon.Inpracticemodel(实践模型)inputisusuallynotknownwithcertainty.Dataarebasedonforecastsand,hen