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1、 第八第八章章 利润最大化和竞争性供给利润最大化和竞争性供给 本章概要本章概要完全竞争市场的利润最大化完全竞争市场的利润最大化以及短期、长期均衡以及短期、长期均衡1假设：厂商追求利润最大化假设：厂商追求利润最大化 不符合三条件不符合三条件定义：完全竞争市场定义：完全竞争市场分析框架：分析框架：结论结论 短期供给线；三种长期供给线短期供给线；三种长期供给线经验研究经验研究符合三条件符合三条件竞争市场利润最大化与均衡竞争市场利润最大化与均衡短短期期均均衡衡：短短期期供供给给线、生产者剩余线、生产者剩余长长期期均均衡衡：长长期期供供给给线线长长期期利利润润最最大大化化受受冲冲击：税收效应击：税收效应
2、21.1厂商追求利润最大化的假设32.1完全竞争市场的定义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：符合下面三个特征的市场称为完全竞争市场：（1）产品同质）产品同质（Product homogeneity）；）；（2）厂商和消费者都是价格接受者）厂商和消费者都是价格接受者（Price taking）；）；（3）厂商无成本进入与退出）厂商无成本进入与退出（Free entry and exit）4IndustryD$4SPrice$per bushelOutput(millions of bushels)100（1）产品同质：存在市场均衡价格P5d$4Output(bushel
3、s)Price$per bushel100200FirmIndustryD$4SPrice$per bushelOutput(millions of bushels)1006d$4Output(bushels)Price$per bushel100200FirmAVCiAVCj7P=MR=AROutput(bushels)Price$per bushel100200Firm2.2完全竞争市场的重要性质完全竞争市场的重要性质8证明93.1.分析框架：数学解分析框架：数学解10q210203040Price50MCAVCAC01234567891011Outputq*AR=MR=PAq1:MR M
4、Cq2:MC MRq*:MC=MR q1Lost Profit for q2q*Lost Profit for q2q*3.2.分析框架：几何解分析框架：几何解11 当当MRMC时时 增加产量所增加的收益大于所增加的成本，因而总增加产量所增加的收益大于所增加的成本，因而总利润可以增加；利润可以增加；当当MRMC时时 减少产量所减少的收益小于所减少的成本，因而总利润减少产量所减少的收益小于所减少的成本，因而总利润可以增加；可以增加；当当MR=MC时时 无论怎样调整产量，总利润都只会减少而不会增加。无论怎样调整产量，总利润都只会减少而不会增加。1210203040Price500123456789
5、1011OutputMCAVCACq*AR=MR=PA4.1.短期均衡短期均衡MR=MC情形情形1：利润为正：利润为正 1310203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形情形2：利润为：利润为01410203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形情形3：弥补全部可变成本之外还能弥补部分固定成本：弥补全部可变成本之外还能弥补部分固定成本1510203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形情形4：刚好弥补全部可变成本，
6、不能弥补一点固定成本：刚好弥补全部可变成本，不能弥补一点固定成本1610203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形情形5：甚至不能弥补全部可变成本，更谈不上弥补一点固定成本：甚至不能弥补全部可变成本，更谈不上弥补一点固定成本17关于短期均衡的总结关于短期均衡的总结短期均衡的条件是：SMC=SMR=P短期均衡中利润可能为正，为零，为负。18Price($perunit)OutputMCAVCACP=AVCP2q2P1q1S4.2.1由短期均衡的五种情形可推导出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：几何完全竞争厂商的短期
7、供给线：几何194.2.2由短期均衡的五种情形可推导出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：数学完全竞争厂商的短期供给线：数学20ProducerProducerSurplusSurplusPrice($perunit ofoutput)OutputAVCAVCMCMCA AB BP Pq q*4.3.1由短期条件理解生产者剩余的定义：几何由短期条件理解生产者剩余的定义：几何CD214.3.2由短期条件理解生产者剩余的定义：数学由短期条件理解生产者剩余的定义：数学22 生产者剩余与经济利润的区别生产者剩余与经济利润的区别23D DP P*q q*ProducerProducer
8、SurplusSurplusPrice($perunit ofoutput)OutputS S 市场的生产者剩余市场的生产者剩余24q1BCADPriceOutputP=MR=AR$40SACSMCq3LACLMC 4.4.1从从长期利润最大化长期利润最大化到长期均衡到长期均衡25PriceOutputP=MR=AR$40q3LACLMC 4.4.2从从长期利润最大化长期利润最大化到到长期均衡长期均衡P=MR=AR$4026 4.5行业的长期供给曲线行业的长期供给曲线27LACSMCq1D1S1Q1P1D2P2P2q2S2Q2OutputOutput$P1SL（1）成本不变行业）成本不变行业2
9、8OutputOutput$D1S1q1P1Q1P1S SL LSMC1LAC1SMC2LAC2P3S2P3Q3q2P2D2Q2P2（2）成本递增行业）成本递增行业29S2SLP3Q3P3SMC2LAC2OutputOutput$P1D1S1P1Q1q1SMC1LAC1q2P2D2Q2P2（3）成本递减行业）成本递减行业30Price($perunit ofoutput)OutputAVC1MC1P1q1t tMC2=MC1+taxAVC24.5长期利润最大化受到税收冲击的情形长期利润最大化受到税收冲击的情形q231 32The Sveriges Riksbank Prize in Econo
10、mic Sciences in Memory of Alfred Nobel 2009Elinor Ostrom 1/2USA Indiana University Bloomington,IN,USAb.1933 for her analysis of economic governance,especially the commons33The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel 2009Oliver E.Williamson1/2USA University of Californi
11、a Berkeley,CA,USA b.1932 for his analysis of economic governance,especially the boundaries of the firm 3435Economic governance:the organization of cooperation Elinor Ostrom has demonstrated how common property can be successfully managed by user associations.Press Release 12 October 200936Oliver Wil
12、liamson has developed a theory where business firms serve as structures for conflict resolution.37Over the last three decades these seminal contributions have advanced economic governance research from the fringe to the forefront of scientific attention.38 Economic transactions take place not only i
13、n markets,but also within firms,associations,households,and agencies.Whereas economic theory has comprehensively illuminated the virtues and limitations of markets,it has traditionally paid less attention to other institutional arrangements.39The research of Elinor Ostrom and Oliver Williamson demon
14、strates that economic analysis can shed light on most forms of social organization.40 Elinor Ostrom has challenged the conventional wisdom that common property is poorly managed and should be either regulated by central authorities or privatized.Based on numerous studies of user-managed fish stocks,
15、pastures,woods,lakes,and groundwater basins,Ostrom concludes that the outcomes are,more often than not,better than predicted by standard theories.41 She observes that resource users frequently develop sophisticated mechanisms for decision-making and rule enforcement to handle conflicts of interest,a
16、nd she characterizes the rules that promote successful outcomes.42Oliver Williamson has argued that markets and hierarchical organizations,such as firms,represent alternative governance structures which differ in their approaches to resolving conflicts of interest.43The drawback of markets is that t
17、hey often entail haggling and disagreement.The drawback of firms is that authority,which mitigates contention,can be abused.Competitive markets work relatively well because buyers and sellers can turn to other trading partners in case of dissent.44 But when market competition is limited,firms are be
18、tter suited for conflict resolution than markets.A key prediction of Williamsons theory,which has also been supported empirically,is therefore that the propensity of economic agents to conduct their transactions inside the boundaries of a firm increases along with the relationship-specific features
19、of their assets.45Elinor Ostrom delivering a lecture at Indiana University,Bloomington,July 2008.46例题例题147484950例题例题25152例题例题35354例题例题35556例题例题45758例题例题5Suppose you are given the following information about a particular industry:Assume that all firms are identical,and that the market is characterize
20、d by pure competition.59例题例题5(1)Find the equilibrium price,the equilibrium quantity,the output supplied by the firm,and the profit of the firm.6061(2)Would you expect to see entry into or exit from the industry in the long-run?Explain.What effect will entry or exit have on market equilibrium?62(2)解：
21、Entry because the firms in the industry are making positive profit.As firms enter,the supply curve for the industry will shift down and to the right and the equilibrium price will fall,all else the same.This will reduce each firms profit down to zero until there is no incentive for further entry.63(
22、3)What is the lowest price at which each firm would sell its output in the long run?Is profit positive,negative,or zero at this price?Explain.6465(4)错题目错题目 What is the lowest price at which each firm would sell its output in the short run?Is profit positive,negative,or zero at this price?Explain.666
23、7例题例题66869例题例题77071例题例题8 Consider a city that has a number of hot dogs stands operating throughout the downtown area.Suppose that each vendor has a marginal cost of$1.50 per hot dog sold,and no fixed cost.Suppose the maximum number of hot dogs any one vendor can sell in a day is 100.72(1)If the pric
24、e of a hot dog is$2,how may hot dogs does each vendor want to sell?Since marginal cost is equal to 1.5 and the price is equal to 2,the hot dog vendor will want to sell as many hot dogs as possible,or in other words,100 hot dogs.73(2)If the industry is perfectly competitive will the price remain at$2
25、 for a hot dog?If not,what will the price be?The price should fall to$1.50 so that price is equal to marginal cost.Each hot dog vendor will have an incentive to lower the price of a hot dog below$2 so they can sell more hot dogs than their competitors.No hot dog vendor will sell a hot dog for a pric
26、e below marginal cost,so the price will fall until it reaches$1.50.74(3)If each vendor sells exactly 100 hot dogs a day and the demand for hot dogs from vendors in the city is Q=4400-1200P,how many vendors are there?If price is 1.50 then Q=4400-1200*1.5=2600 in total.If each vendor sells 100 hot dog
27、s then there are 26 vendors.75(4)Suppose the city decides to regulate hot dog vendors by issuing permits.If the city issues only 20 permits,and if each vendor continues to sell 100 hot dogs a day,what price will a hot dog sell for?If there are 20 vendors selling 100 hot dogs each then the total numb
28、er sold is 2000.If Q=2000 then P=$2,from the demand curve.76(5)Suppose the city decided to sell the permits.What is the highest price a vendor would pay for a permit?At the new price of$2 per hot dog the vendor is making a profit of$0.50 per hot dog,or a total of$50.This is the most they would pay o
29、n a per day basis.77例题例题9 A sales tax of$1 per unit of output is placed on one firm whose product sells for$5 in a competitive industry.78(1)How will this tax affect the cost curves for the firm?With the imposition of a$1 tax on a single firm,all its cost curves shift up by$1.Total cost becomes TC+t
30、q,or TC+q since t=1.Average cost is now AC+1.Marginal cost is now MC+1.79(2)What will happen to the firms price,output,and profit?Since the firm is a price-taker in a competitive market,the imposition of the tax on only one firm does not change the market price.Since the firms short-run supply curve
31、 is its marginal cost curve above average variable cost and that marginal cost curve has shifted up(inward),the firm supplies less to the market at every price.Profits are lower at every quantity.80(3)Will there be entry or exit in the industry?If the tax is placed on a single firm,that firm will go
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