北大院微观课件

200520051ChapterFive25.15.2ChapterFive25.15.2AssumptionsofPerfectlyCompetitiveMarkets5.3TheOptimalOutputDecisionintheShortRun5.4TheOptimalOutputDecisionintheLongRun5.5TheEvaluationsofaCompetitiveNicholson:ChapterNicholson:Chapter13,P334-3ReadingsaboutthepartofthischapterChapterFive45.15.2ChapterFive45.15.2AssumptionsofPerfectlyCompetitiveMarkets5.3TheOptimalOutputDecisionintheShortRun5.4TheOptimalOutputDecisionintheLongRun5.5TheEvaluationsofaCompetitiveTheDeterminantofFirmHowdoesafirmdecidehowmuchtosupplyTheDeterminantofFirmHowdoesafirmdecidehowmuchtosupplyatagivenprice?Thisdependsuponthefirm’smarketenvironmentcompetitors’MarketEnvironmentAretheremanyMarketEnvironmentAretheremanyotherHowdootherfirms’decisionseffectthefirm’spayoffs?MarketEnvironmentMonopoly(垄断市场JustonethatMarketEnvironmentMonopoly(垄断市场JustonethatdeterminestheOligopoly（寡头市场Anumberoffirmsthedecisionsofeachinfluencingthepayoffs（得益）ofotherMarketEnvironmentMonopolisticCompetition（ManyfirmsMarketEnvironmentMonopolisticCompetition（ManyfirmseachmakingslightlydifferentEachoutputlevelissmallrelativetothePerfectCompetition（完全竞争市场）:Manyfirms,allmakingthesameproduct.Eachfirm’soutputlevelissmallrelativetothetotaloutputlevel.TheFourTypesofMarket9 TheFourTypesofMarket9 Profit（利润最大化EachfirmisProfit（利润最大化Eachfirmisaprofit-Eachfirmchooseitsoutputlevelbyp=istheinversedemandfunction（反ProfitThenecessaryconditionforchoosingthevalueofqthatmaximizesprofitsis:dp=p'(q)=dTR(ProfitThenecessaryconditionforchoosingthevalueofqthatmaximizesprofitsis:dp=p'(q)=dTR(q)-dTC(q)=Thefirst-orderconditionforamaximumisMR=dTR==ProfitThesecondconditionisddp<=dProfitThesecondconditionisddp<=d<=-\MR'(q)<MCProfitMaximization:AnGraphicComparingTR(q)and$(perQuestion:WhyisprofitnegativewhenoutputisProfitMaximization:AnGraphicComparingTR(q)and$(perQuestion:WhyisprofitnegativewhenoutputisADBC0pOutput(unitsperMarginalRevenue,MarginalCost,andProfitMaximizationComparingTR(q)andTR’(q)>MarginalRevenue,MarginalCost,andProfitMaximizationComparingTR(q)andTR’(q)>MR>profitathigher$(perABq00ProfitispOutput(unitsperMarginalRevenue,MarginalCost,andProfitMaximization$(perComparingTR(q)OutputlevelsMarginalRevenue,MarginalCost,andProfitMaximization$(perComparingTR(q)OutputlevelsTR’(q)<MR<ProfitisAB0pOutput(unitsperMarginalRevenue,MarginalCost,andProfitMaximization$(perWhyisprofitAwhenmoreorMarginalRevenue,MarginalCost,andProfitMaximization$(perWhyisprofitAwhenmoreorlessthanB0pOutput(unitsperMarginalRevenue,MarginalCost,andProfitMaximizationComparingTR(q)andOutputlevel:TR’(q)=MRMarginalRevenue,MarginalCost,andProfitMaximizationComparingTR(q)andOutputlevel:TR’(q)=MR=Profitis$(perAB0pOutput(unitsperMarginalRevenue,MarginalCost,andProfitMaximization$(perTherefore,itcanbeProfitsareMC=MR.MarginalRevenue,MarginalCost,andProfitMaximization$(perTherefore,itcanbeProfitsareMC=MR.AB0pOutput(unitsperTheMarginalRevenue/MarginalCostAttheTheMarginalRevenue/MarginalCostAttheprofitmaximizinglevelofMarginalRevenue=MarginalMR=Firms,startingatzerooutput,canexpandoutputsolongasmarginalrevenueexceedsmarginalcost,butdon’tgobeyondthepointwherethesetwoareequal.andMR（边际收益）TR=TR(q)=AR=TRandMR（边际收益）TR=TR(q)=AR=TRpq=qqMR=dTR=p(11)ChapterFiveChapterFiveAssumptionsofPerfectThereareAssumptionsofPerfectTherearemanybuyersandsellers（有许多买者和卖者）,i.e.noonefirmcandominate/influencethefirmsarepriceHomogeneousproduct（同质产品Freedomofentryandexit（进入与退出自由PerfectlyCompetitive(Assumption1)TherearePerfectlyCompetitive(Assumption1)TherearemanybuyersandsellersTheindividualfirmsellsaverysmallshareofthetotalmarketoutputand,therefore,cannotinfluencemarketprice.Theindividualconsumerbuystoosmallashareofindustryoutputtohaveanyimpactonmarketprice.PerfectlyCompetitive(AssumptionEachsellerPerfectlyCompetitive(AssumptionEachselleristoosmalltoaffectthesellerscansellalltheycanproduceatthemarketprice.sellerscansellnothingabovethemarketsellershavenoincentivetoofferanythingbelowmarketprice.PerfectlyCompetitive (Assumption2ProductPerfectlyCompetitive (Assumption2ProductHomogeneity产品同Theproductsofallfirmsareperfectbuyersdon’tcarewhereproductcomesAgriculturalproducts(wheat,riceandcorn),oil,copper,iron,lumberPerfectlyCompetitive(Assumption3FreeEntryPerfectlyCompetitive(Assumption3FreeEntryandExit（自 Buyerscaneasilyswitchfromonesuppliertoanother.SupplierscaneasilyenterorexitaPerfect(Assumption4Perfectinformation完全 Perfect(Assumption4Perfectinformation完全 PerfectknowledgeallpartsofbuyersPerfectlyCompetitiveDiscussionWhatarePerfectlyCompetitiveDiscussionWhataresomebarrierstoentryandAreallmarketsWhenisamarkethighlyPerfectthedemandcurvefacedbyPerfectthedemandcurvefacedbythefirmTheDemandCurveofPerfectlyCompetitiveMarketsPMarketTheDemandCurveofPerfectlyCompetitiveMarketsPMarketMarketQTheDemandCurveofPerfectlyCompetitiveMarketsPMarketAtapriceofp’,zeroisdemandedTheDemandCurveofPerfectlyCompetitiveMarketsPMarketAtapriceofp’,zeroisdemandedfromthefirm.MarketQTheDemandCurveofPerfectlyCompetitiveMarketsPMarketAtapriceofp’,zeroisdemandedTheDemandCurveofPerfectlyCompetitiveMarketsPMarketAtapriceofp’,zeroisdemandedfromthefirm.MarketQAtapriceofp”thefirmfacestheentiremarketdemand.FromMarketDemandCurvetothedemandcurvefacedbythefirmPqFirm’sDemandFromMarketDemandCurvetothedemandcurvefacedbythefirmPqFirm’sDemandQ MarginalRevenueinthecompetitiveAMarginalRevenueinthecompetitiveApricetakerisafirmorindividualwhosedecisionsregardingbuyingorsellinghavenoeffectontheprevailingmarketpriceofagoodorservice.ForapricetakingAR=MR=MarginalRevenue,MarginalCost,andProfitMaximizationinthecompetitivefirmTheMarginalRevenue,MarginalCost,andProfitMaximizationinthecompetitivefirmThecompetitivefirm’sChapterFiveChapterFiveChoosingOutputintheShortChoosingOutputintheShortWewillcombineproductionandcostanalysiswithdemandtodetermineoutputandprofitability.Max.ProfitWhentheFirmisaprice-PqMax.ProfitWhentheFirmisaprice-PqMax.ProfitWhentheFirmisaprice-Thefirst-ordermaximumprofitMax.ProfitWhentheFirmisaprice-Thefirst-ordermaximumprofitconditionThatSoataprofitmaximumwithq*>0,marketpricepequalsthemarginalcostofproductionatq=q*.ChoosingOptimalOutputintheShortRun:TRandTC0qMR=0MC>MC<MC=ChoosingOptimalOutputintheShortRun:TRandTC0qMR=0MC>MC<MC=MC>ChoosingOptimalOutputintheShortRun:MRandMC($perLostprofitLostprofitq2><ADCBq1:MR>SMCqChoosingOptimalOutputintheShortRun:MRandMC($perLostprofitLostprofitq2><ADCBq1:MR>SMCq2:SMC>Mq0:SMC=MRSMCfalli01789023456TheFirm’sOptimalDecisionanditsExcessProfitTheFirm’sOptimalDecisionanditsExcessProfitP1>SAC→p>0(ExcessAMR=P1C0P1>SAC→p>0(ExcessAMR=P1C0qBP2=SAC→p=0(butthereisnormalprofit)AAR=MR=P2q0P2=SAC→p=0(butthereisnormalprofit)AAR=MR=P2q0SAVC<P3<SAC→p<0(thereisloss,butP3cancoverallaveragevariablecostandapartofSAVC<P3<SAC→p<0(thereisloss,butP3cancoverallaveragevariablecostandapartofFC,SothefirmwillBCP0q3P4=SAVC→p<0ApointisBCAMR=q0P4=SAVC→p<0ApointisBCAMR=q0P5<SAVC→p<0(thereisgreatloss,andP5cannotcoverapartofaveragevariablecostandallFC,Sothefirmwillproducenooutput)BCP5<SAVC→p<0(thereisgreatloss,andP5cannotcoverapartofaveragevariablecostandallFC,Sothefirmwillproducenooutput)BCMR=Aq0TheShutdownDecision(停工决策):AnAlgebraMethodProfitsareTheShutdownDecision(停工决策):AnAlgebraMethodProfitsaregivenp=TR-STC=pq-SFC-Ifq=0,STVCandTotalRevenuesare0,Thefirmwillproducesomethingonlyifp>-SFC,ButthatmeansthatTheShutdownThefirmwilloptforq>0TheShutdownThefirmwilloptforq>0 q‡STVCor,dividingbyq,STVCP=SAVC‡qThepricemustexceedaveragevariableTheShutdownTheshutdownpriceisTheShutdownTheshutdownpriceisthepricebelowwhichthefirmwillchoosetoproducenooutputintheshort-run.Itisequaltominimumaveragevariablecosts.ChoosingOutputintheShortChoosingOutputintheShortProfitismaximizedwhenSMC=IfP>SACthefirmismakingIfSAVC<P<SACthefirmshouldproduceataloss.IfP<SAVC<SACthefirmshouldshut-TheConditionsforChoosingOptimalOutputintheShortRunTheConditionsforChoosingOptimalOutputintheShortRunShutDownq0ShutDownq0ACompetitiveFirm’sShort-RunSupplyCurveP=MR=ACompetitiveFirm’sShort-RunSupplyCurveP=MR=MC——MAXP=MCfiP=MC(q)——短期供给曲Supplyistheamountofoutputforeverypossibleprice.Therefore:IfP=P1,thenq=q1;IfP=P2,thenq=IfP=P3,thenq=q3;IfP=P4,thenq=Firm’sShutDownq0Firm’sShutDownq0ACompetitiveFirm’sShort-RunSupplyCurveInACompetitiveFirm’sShort-RunSupplyCurveInaboveFigure,theshutdownpriceisForallP‡P4,thefirmwillfollowthe=MCrule,sothesupplycurvewillbetheshort-runmarginalcostcurve.TheFirm’sShort-RunSupplyCurve_SummaryThefirm’sTheFirm’sShort-RunSupplyCurve_SummaryThefirm’sshort-runsupplycurveisrelationshipbetweenpriceandquantitysuppliedbyafirmintheshort-run.Foraprice-takingfirm,thisisthepositivelyslopedportionoftheshort-runmarginalcostForallpossibleprices,themarginalcostcurveshowshowmuchoutputthefirmshouldsupply.ACompetitiveFirm’sShort-RunSupplyCurveSupplyisACompetitiveFirm’sShort-RunSupplyCurveSupplyisupwardslopingduetodiminishingreturnsHigherpricecompensatesthefirmforhighercostofadditionaloutputandincreasestotalprofitbecauseitappliestoallunits.HowtogetSupplyFunction:AnExampleAssumeafirm’scostHowtogetSupplyFunction:AnExampleAssumeafirm’scostfunctionSTC=0.1q3-2q2+15qWhatisthisfirm’sSRsupply4+12P-S=FromtheSRindividualSupplyCurveFromtheSRindividualSupplyCurveSRMarketSupplyTheshort-runmarketsupplycurveshowstheamountofoutputthattheindustrywillproduceintheshort-runforeverypossibleprice.SRMarketSupplyCurve:HoldInputPriceconstantwhenoutputincreasesSRMarketSupplyCurve:HoldInputPriceconstantwhenoutputincreasesShortRunpe