竞争市场利润最大化与均衡中央财经大学张苏

11.1厂商追求利润最大化的假设22.1完全竞争市场的定义

符合下面三个特征的市场称为完全竞争市场：（1）产品同质（Producthomogeneity）；（2）厂商和消费者都是价格接受者（Pricetaking）；（3）厂商无成本进入与退出（Freeentryandexit）3IndustryD$4SPrice$perbushelOutput(millionsofbushels)100（1）产品同质：存在市场均衡价格P4d$4Output(bushels)Price$perbushel100200Firm（个别公司）Industry(整个产业）D$4SPrice$perbushelOutput(millionsofbushels)100在完全竞争市场上，单个生产者的生产的产品价格是不受市场需求影响的，从而使得产品的价格不随需求量的变化而变化。5d$4Output(bushels)Price$perbushel100200FirmAVCiAVCj市场均价P=46P=MR=AROutput(bushels)Price$perbushel100200Firm2.2完全竞争市场的重要性质7证明R（q）总收入完全竞争市场上某企业的产品市场均价和产量是没有关系的83.1.分析框架：数学解π（q）：利润利润取到极大值的三个数学条件9q210203040Price50MCAVCAC01234567891011Outputq*AR=MR=PAq1:MR>MCq2:MC>MRq*:MC=MRq1LostProfitforq2>q*LostProfitforq2>q*3.2.分析框架：几何解A点为利润最大化的点，因为在A点MC=MR,因此q*对应的R线与TC线所分别对应的值的差为正值的最大值1010203040Price5001234567891011OutputMCAVCACq*AR=MR=PA4.1.短期均衡MR=MC情形1：利润为正1110203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形2：利润为0A点为盈亏平衡点（此时，在平均收入不变的情况下，虽然不能盈利，但是继续生产能弥补一部分固定成本）B点为停止生产点（此时，在平均收入不变的情况下，必须停产，若继续生产，会使得总成本不断增加）AR=MR=PB12

当MR>MC时增加产量所增加的收益大于所增加的成本，因而总利润可以增加；当MR<MC时减少产量所减少的收益小于所减少的成本，因而总利润可以增加；当MR=MC时无论怎样调整产量，总利润都只会减少而不会增加。1310203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形3：弥补全部可变成本之外还能弥补部分固定成本AC—AVC=固定成本固定成本可变成本1410203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形4：刚好弥补全部可变成本，不能弥补一点固定成本1510203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形5：甚至不能弥补全部可变成本，更谈不上弥补一点固定成本16关于短期均衡的总结短期均衡的条件是：SMC=SMR=P短期均衡中利润可能为正，为零，为负。17Price($perunit)OutputMCAVCACP=AVCP2q2P1q1S4.2.1由短期均衡的五种情形可推导出

完全竞争厂商的短期供给线：几何该点为生产停止点184.2.2由短期均衡的五种情形可推导出

完全竞争厂商的短期供给线：数学19ProducerSurplusPrice($perunitofoutput)OutputAVCMCABPq*4.3.1由短期条件理解生产者剩余的定义：几何CD204.3.2由短期条件理解生产者剩余的定义：数学21

生产者剩余与经济利润的区别生产者剩余经济利润22DP*q*ProducerSurplusPrice($perunitofoutput)OutputS

市场的生产者剩余23q1BCADPriceOutputP=MR=AR$40SACSMCq3LACLMC

4.4.1从长期利润最大化到长期均衡24PriceOutputP=MR=AR$40q3LACLMC

4.4.2从长期利润最大化到长期均衡P=MR=AR$40生产利润不为零，更多的厂商加入生产，导致市场价格水平下降，P线下移生产利润为负，生产商离开市场，P线上移AA点为长期均衡点，共有5条线经过该店25

4.5行业的长期供给曲线26LACSMCq1D1S1Q1P1D2P2P2q2S2Q2OutputOutput$$P1SL（1）成本不变行业27OutputOutput$$D1S1q1P1Q1P1SLSMC1LAC1SMC2LAC2P3S2P3Q3q2P2D2Q2P2（2）成本递增行业长期供给曲线28S2SLP3Q3P3SMC2LAC2OutputOutput$$P1D1S1P1Q1q1SMC1LAC1q2P2D2Q2P2（3）成本递减行业29Price($perunitofoutput)OutputAVC1MC1P1q1tMC2=MC1+taxAVC24.5长期利润最大化受到税收冲击的情形q230

31例题132333435例题23637例题33839例题34041例题44243例题5Supposeyouaregiventhefollowinginformationaboutaparticularindustry:

Assumethatallfirmsareidentical,andthatthemarketischaracterizedbypurecompetition.44例题5(1)Findtheequilibriumprice,theequilibriumquantity,theoutputsuppliedbythefirm,andtheprofitofthefirm.均衡价格均衡产量工厂产量利润4546(2)Wouldyouexpecttoseeentryintoorexitfromtheindustryinthelong-run?Explain.Whateffectwillentryorexithaveonmarketequilibrium?47(2)解：Entrybecausethefirmsintheindustryaremakingpositiveprofit.Asfirmsenter,thesupplycurvefortheindustrywillshiftdownandtotherightandtheequilibriumpricewillfall,allelsethesame.Thiswillreduceeachfirm’sprofitdowntozerountilthereisnoincentiveforfurtherentry.48(3)Whatisthelowestpriceatwhicheachfirmwouldsellitsoutputinthelongrun?Isprofitpositive,negative,orzeroatthisprice?Explain.

4950(4)错题目Whatisthelowestpriceatwhicheachfirmwouldsellitsoutputintheshortrun?Isprofitpositive,negative,orzeroatthisprice?Explain.

5152例题65354例题75556例题8

Consideracitythathasanumberofhotdogsstandsoperatingthroughoutthedowntownarea.Supposethateachvendorhasamarginalcostof$1.50perhotdogsold,andnofixedcost.Supposethemaximumnumberofhotdogsanyonevendorcansellinadayis100.57(1)Ifthepriceofahotdogis$2,howmayhotdogsdoeseachvendorwanttosell?Sincemarginalcostisequalto1.5andthepriceisequalto2,thehotdogvendorwillwanttosellasmanyhotdogsaspossible,orinotherwords,100hotdogs.58(2)Iftheindustryisperfectlycompetitivewillthepriceremainat$2forahotdog?Ifnot,whatwillthepricebe?Thepriceshouldfallto$1.50sothatpriceisequaltomarginalcost.Eachhotdogvendorwillhaveanincentivetolowerthepriceofahotdogbelow$2sotheycansellmorehotdogsthantheircompetitors.

Nohotdogvendorwillsellahotdogforapricebelowmarginalcost,sothepricewillfalluntilitreaches$1.50.59(3)Ifeachvendorsellsexactly100hotdogsadayandthedemandforhotdogsfromvendorsinthecityisQ=4400-1200P,howmanyvendorsarethere?Ifpriceis1.50thenQ=4400-1200*1.5=2600intotal.Ifeachvendorsells100hotdogsthenthereare26vendors.60(4)Supposethecitydecidestoregulatehotdogvendorsbyissuingpermits.Ifthecityissuesonly20permits,andifeachvendorcontinuestosell100hotdogsaday,whatpricewillahotdogsellfor?Ifthereare20vendorsselling100hotdogseachthenthetotalnumbersoldis2000.IfQ=2000thenP=$2,fromthedemandcurve.61(5)Supposethecitydecidedtosellthepermits.Whatisthehighestpriceavendorwouldpayforapermit?Atthenewpriceof$2perhotdogthevendorismakingaprofitof$0.50perhotdog,oratotalof$50.Thisisthemosttheywouldpayonaperdaybasis.62例题9

Asalestaxof$1perunitofoutputisplacedononefirmwhoseproductsellsfor$5inacompetitiveindustry.

63(1)Howwillthistaxaffectthecostcurvesforthefirm?Withtheimpositionofa$1taxonasinglefirm,allitscost