课件大纲中级微观济学

北京大学北京大学国家发展研究院2011年秋季学本科双学位课中级微观经济学(2第二十一讲：交第三十一第三十一章Exchange交TheEdgeworthBoxParetoimprovingtradeParetoEfficientAllocationTradeinacompetitivemarketWalras’Lawofgeneralequilibrium一般均衡的瓦FirstFundamentalTheoremofWelfareEconomicsSecondFundamentalTheoremofWelfareEconomics•••••••Twoconsumers,Aandendowmentsofgoods1andareTwoconsumers,Aandendowmentsofgoods1andare(A,AandB(B,B121B(2(6,4)ThetotalquantitiesAB62unitsofgoodunitsofgood11andAB4222StartinganEdgeworthHeightAStartinganEdgeworthHeightA242AB62Width11Thedimensionsoftheboxaretheofthegoods.FeasibleFeasibleWhatallocationsofthe8unitsofgood1andthe6unitsofgood2areHowcanallofthefeasibleallocationsbedepictedbytheEdgeworthboxdiagram?Onefeasibleallocationisthebefore-tradeallocation;i.e.theendowment1A22221A22221A11OtherFeasible(xA,xA)denotesanallocationOtherFeasible(xA,xA)denotesanallocation12(xB,xB)denotesanallocation12AnallocationisfeasibleifandonlyxAxBA1111xAxBAB.2222FeasibleFeasibleAllpointsinthebox,includingtheboundary,representfeasibleallocationsofthecombinedWhichallocationswillbeblockedbyoneorbothconsumers?Whichallocationsmakebothconsumersbetteroff?Forconsumer2Forconsumer2211Forconsumer2Forconsumer2211ForconsumerB1ForconsumerB1222B122B1221122B12B122112Pareto-Pareto-AnallocationoftheendowmentthatimprovesthewelfareofaconsumerwithoutreducingthewelfareofanotherisaPareto-improvingWherearethePareto-improvingAPareto-x2B1APareto-x2B12ThesetofPareto-2112Pareto-ThemarginalRatesofSubstitutionPareto-ThemarginalRatesofSubstitutionareequalsTheallocationPareto-optimalsincetheonlywayoneconsumer’swelfarecanbeincreasedistodecreasethewelfareoftheotherAlltheallocationsmarked2aarePareto-BAlltheallocationsmarked2aarePareto-B122112contractcurve契约曲isthesetofallPareto-optimalallocations.2contractcurve契约曲isthesetofallPareto-optimalallocations.2B12Thecontract2112Pareto-ButtowhichofthemanyallocationsonPareto-ButtowhichofthemanyallocationsonthecontractcurvewillconsumersThatdependsuponhowtradeisInperfectlycompetitivemarkets?one-on-onebargaining?TheCore核2B1TheCore核2B12ThesetofPareto-2112ThePareto-optimaltradesblockedbyB21O1BThePareto-optimaltradesblockedbyB21O1B2211Pareto-optimaltradesblockedbyA2Pareto-optimaltradesnotblockedbyAorBarethecore.2B1Pareto-optimaltradesnotblockedbyAorBarethecore.2B122112TheTheThecoreisthesetofallPareto-optimalallocationsthatarewelfare-improvingforbothconsumersrelativetotheirownendowments.RationaltradeshouldachieveacoreButwhichcoreAgain,thatdependsuponthemannerinwhichtradeisconducted.TradeinTradeinCompetitiveConsidertradeinperfectlycompetitivemarkets.Eachconsumerisaprice-takertryingtomaximizeherownutilitygivenp1,p2andherownendowment.is,...TradeinCompetitiveForconsumer2pxApTradeinCompetitiveForconsumer2pxApAp 22111Forconsumer2pxBpBForconsumer2pxBpB 22111TradeinCompetitiveSogivenp1andp2,consumerB’snetdemandsforcommodities1and2TradeinCompetitiveSogivenp1andp2,consumerB’snetdemandsforcommodities1and2arex*BB.x*B2211Ageneralequilibriumoccurswhenpricesp1andp2causeboththemarketsforcommodities1and2toclear;i.e.x*AA1111x*AAB2222CanthisPOallocationbe2B1CanthisPOallocationbe2B122112Budgetconstraintforconsumer2B1Budgetconstraintforconsumer2B12A2211221B122A221B122A2211Budgetconstraintforconsumer2TradeinCompetitivex*ATradeinCompetitivex*AA1111x*AA2222Soatthegivenpricesp1andp2thereisanexcesssupplyofcommodity1excessdemandforcommodityNeithermarketclearssothepricesp1andp2donotcauseageneralequilibrium.TradeTradeinCompetitiveSincethereisanexcessdemandforcommodity2,p2willrise.Sincethereisanexcesssupplyofcommodity1,p1willfall.Theslopeofthebudgetconstraintsis-p1/p2sothebudgetconstraintswillpivotabouttheendowmentpointandbecomelesssteep.2B12B12211221B12221B1222112TradeinCompetitivex*ATradeinCompetitivex*AA2222x*AA1111Atthenewpricesp1andp2bothmarketsclear;thereisageneralequilibrium.TradingincompetitivemarketsachievesaparticularPareto-optimalallocationoftheThisisanexampleoftheFirstFundamentalTheoremofWelfareFirstFirstFundamentalTheoremWelfareGiventhatconsumers’preferencesarewell-behaved,tradinginperfectlycompetitivemarketsimplementsaPareto-optimalallocationoftheeconomy’sendowment.竞争性的市场能够达到帕累托效率的结ImplicitImplicitNoconsumptionexternality(外部效应AgentsbehaveEquilibrium市场失灵问SecondSecondFundamentalTheoremWelfareAnyPareto-optimalallocation(i.e.anypointonthecontractcurve)canbeachievedbytradingincompetitivemarketsprovidedthatendowmentsarefirstappropriatelyrearrangedamongsttheconsumers.ForanyPareto-optimalallocationtherearepricesandanallocationofendowmentthatmakesthePareto-optimalallocationSecondFundamental2B1SecondFundamental2B12Thecontract2112SecondFundamentalImplementedbycompetitivetradingfromtheendowment.2B11SecondFundamentalImplementedbycompetitivetradingfromtheendowment.2B11x*A2222x*A1112SecondFundamentalCanthisallocationbeimplementedbycompetitivetradingSecondFundamentalCanthisallocationbeimplementedbycompetitivetradingfrom?2B122112SecondFundamentalButthisallocationisimplementedbycompetitivetradingfrom.2SecondFundamentalButthisallocationisimplementedbycompetitivetradingfrom.2B122112ImplicationsofImplicationsofthe2ndMarketequilibriumisdistributionallyRedistributioncanbecarriedoutforThemarketplaysonlytheallocationWalras’Walras’Walras’Lawisanidentity恒等 i.e.astatementthatistrueforanypositiveprices(p1,p2),whethertheseareequilibriumpricesornot.Everyconsumer’spreferencesarewell-behavedso,foranypositiveprices(p1,p2),eachconsumerspendsallofhisbudget.Walras’Forconsumerpx*ApA Forconsumer Walras’Forconsumerpx*ApA Forconsumer px*Bx*BpB Summing p1(x*Ax*B)x*B11222p1(B)(BB11222p1(x*Ax*BAB)1111p2x*BAB)2222Walras’p1(x*AAWalras’p1(x*AAB)1111p2AB