競爭市場利潤最大化與均衡中央財經(jīng)大學張?zhí)K

11.1廠商追求利潤最大化的假設22.1完全競爭市場的定義

符合下面三個特征的市場稱為完全競爭市場：（1）產(chǎn)品同質(zhì)（Producthomogeneity）；（2）廠商和消費者都是價格接受者（Pricetaking）；（3）廠商無成本進入與退出（Freeentryandexit）3IndustryD$4SPrice$perbushelOutput(millionsofbushels)100（1）產(chǎn)品同質(zhì)：存在市場均衡價格P4d$4Output(bushels)Price$perbushel100200Firm（個別公司）Industry(整個產(chǎn)業(yè)）D$4SPrice$perbushelOutput(millionsofbushels)100在完全競爭市場上，單個生產(chǎn)者的生產(chǎn)的產(chǎn)品價格是不受市場需求影響的，從而使得產(chǎn)品的價格不隨需求量的變化而變化。5d$4Output(bushels)Price$perbushel100200FirmAVCiAVCj市場均價P=46P=MR=AROutput(bushels)Price$perbushel100200Firm2.2完全競爭市場的重要性質(zhì)7證明R（q）總收入完全競爭市場上某企業(yè)的產(chǎn)品市場均價和產(chǎn)量是沒有關系的83.1.分析框架：數(shù)學解π（q）：利潤利潤取到極大值的三個數(shù)學條件9q210203040Price50MCAVCAC01234567891011Outputq*AR=MR=PAq1:MR>MCq2:MC>MRq*:MC=MRq1LostProfitforq2>q*LostProfitforq2>q*3.2.分析框架：幾何解A點為利潤最大化的點，因為在A點MC=MR,因此q*對應的R線與TC線所分別對應的值的差為正值的最大值1010203040Price5001234567891011OutputMCAVCACq*AR=MR=PA4.1.短期均衡MR=MC情形1：利潤為正1110203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形2：利潤為0A點為盈虧平衡點（此時，在平均收入不變的情況下，雖然不能盈利，但是繼續(xù)生產(chǎn)能彌補一部分固定成本）B點為停止生產(chǎn)點（此時，在平均收入不變的情況下，必須停產(chǎn)，若繼續(xù)生產(chǎn)，會使得總成本不斷增加）AR=MR=PB12

當MR>MC時增加產(chǎn)量所增加的收益大于所增加的成本，因而總利潤可以增加；當MR<MC時減少產(chǎn)量所減少的收益小于所減少的成本，因而總利潤可以增加；當MR=MC時無論怎樣調(diào)整產(chǎn)量，總利潤都只會減少而不會增加。1310203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形3：彌補全部可變成本之外還能彌補部分固定成本AC—AVC=固定成本固定成本可變成本1410203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形4：剛好彌補全部可變成本，不能彌補一點固定成本1510203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形5：甚至不能彌補全部可變成本，更談不上彌補一點固定成本16關于短期均衡的總結短期均衡的條件是：SMC=SMR=P短期均衡中利潤可能為正，為零，為負。17Price($perunit)OutputMCAVCACP=AVCP2q2P1q1S4.2.1由短期均衡的五種情形可推導出

完全競爭廠商的短期供給線：幾何該點為生產(chǎn)停止點184.2.2由短期均衡的五種情形可推導出

完全競爭廠商的短期供給線：數(shù)學19ProducerSurplusPrice($perunitofoutput)OutputAVCMCABPq*4.3.1由短期條件理解生產(chǎn)者剩余的定義：幾何CD204.3.2由短期條件理解生產(chǎn)者剩余的定義：數(shù)學21

生產(chǎn)者剩余與經(jīng)濟利潤的區(qū)別生產(chǎn)者剩余經(jīng)濟利潤22DP*q*ProducerSurplusPrice($perunitofoutput)OutputS

市場的生產(chǎn)者剩余23q1BCADPriceOutputP=MR=AR$40SACSMCq3LACLMC

4.4.1從長期利潤最大化到長期均衡24PriceOutputP=MR=AR$40q3LACLMC

4.4.2從長期利潤最大化到長期均衡P=MR=AR$40生產(chǎn)利潤不為零，更多的廠商加入生產(chǎn)，導致市場價格水平下降，P線下移生產(chǎn)利潤為負，生產(chǎn)商離開市場，P線上移AA點為長期均衡點，共有5條線經(jīng)過該店25

4.5行業(yè)的長期供給曲線26LACSMCq1D1S1Q1P1D2P2P2q2S2Q2OutputOutput$$P1SL（1）成本不變行業(yè)27OutputOutput$$D1S1q1P1Q1P1SLSMC1LAC1SMC2LAC2P3S2P3Q3q2P2D2Q2P2（2）成本遞增行業(yè)長期供給曲線28S2SLP3Q3P3SMC2LAC2OutputOutput$$P1D1S1P1Q1q1SMC1LAC1q2P2D2Q2P2（3）成本遞減行業(yè)29Price($perunitofoutput)OutputAVC1MC1P1q1tMC2=MC1+taxAVC24.5長期利潤最大化受到稅收沖擊的情形q230

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

Assumethatallfirmsareidentical,andthatthemarketischaracterizedbypurecompetition.44例題5(1)Findtheequilibriumprice,theequilibriumquantity,theoutputsuppliedbythefirm,andtheprofitofthefirm.均衡價格均衡產(chǎn)量工廠產(chǎn)量利潤4546(2)Wouldyouexpecttoseeentryintoorexitfromtheindustryinthelong-run?Explain.Whateffectwillentryorexithaveonmarketequilibrium?47(2)解：Entrybecausethefirmsintheindustryaremakingpositiveprofit.Asfirmsenter,thesupplycurvefortheindustrywillshiftdownandtotherightandtheequilibriumpricewillfall,allelsethesame.Thiswillreduceeachfirm’sprofitdowntozerountilthereisnoincentiveforfurtherentry.48(3)Whatisthelowestpriceatwhicheachfirmwouldsellitsoutputinthelongrun?Isprofitpositive,negative,orzeroatthisprice?Explain.

4950(4)錯題目Whatisthelowestpriceatwhicheachfirmwouldsellitsoutputintheshortrun?Isprofitpositive,negative,orzeroatthisprice?Explain.

5152例題65354例題75556例題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例題9

Asalestaxof$1perunitofoutputisplacedononefirmwhoseproductsellsfor$5inacompetitiveindustry.

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