8第八章竞争市场利润最大化与均衡中央财经大学张苏.ppt

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11.1厂商追求利润最大化的假设22.1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 ））3IndustryD$4SPrice$ per bushelOutput (millions of bushels)100（1）产品同质：存在市场均衡价格P4d$4Output (bushels)Price$ per bushel100200Firm（个别公司）（个别公司）Industry(整个产业）整个产业）D$4SPrice$ per bushelOutput (millions of bushels)100在完全竞争市场上，单个生产者的生产的产品价格是在完全竞争市场上，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。

量的变化而变化5d$4Output (bushels)Price$ per bushel100200FirmAVCiAVCj市场均价市场均价P=46P=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7证明R（（q）总收入）总收入完全竞争市场上某企业的产品市场均价产品市场均价和产量产量是没有关系的83.1.分析框架：数学解分析框架：数学解π（q）：利润利润取到极大值的三个数学条件利润取到极大值的三个数学条件9q210203040Price50MCAVCAC01234567891011Outputq*AR=MR=PAq1 : MR > MCq2: MC > MRq*: MC = MR q1Lost Profit for q2>q*Lost Profit for q2>q*3.2.分析框架：几何解分析框架：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1010203040Price5001234567891011OutputMCAVCACq*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 1110203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形情形2：利润为：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）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）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 •当当MR>MC时时• 增加产量所增加的收益大于所增加的成本，因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；而总利润可以增加；•当当MR

增加1310203040Price5001234567891011OutputMCAVCACq*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AC—AVC=固定成本固定成本固定成本可变成本可变成本1410203040Price5001234567891011OutputMCAVCACq*AR=MR=PA情形情形4：刚好弥补全部可变成本，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1510203040Price5001234567891011OutputMCAVCACq*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16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17Price($ 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供给线：几何该点为生产停止点该点为生产停止点184.2.2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19ProducerProducerSurplusSurplusPrice($ 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CD204.3.2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21 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生产者剩余生产者剩余经济利润经济利润22D DP P* *q q* *ProducerProducerSurplusSurplusPrice($ perunit ofoutput)OutputS S 市场的生产者剩余市场的生产者剩余23q1BCADPriceOutputP = 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24PriceOutputP = 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$40生产利润不为零，更生产利润不为零，更多的厂商加入生产，多的厂商加入生产，导致市场价格水平下导致市场价格水平下降，降，P线下移线下移生产利润为负，生生产利润为负，生产商离开市场，产商离开市场，P线上移线上移AA点为长期均衡点，点为长期均衡点，共有共有5条线经过该条线经过该店店25 4.5行业的长期供给曲线行业的长期供给曲线26LACSMCq1D1S1Q1P1D2P2P2q2S2Q2OutputOutput$$P1SL（（1）成本不变行业）成本不变行业27OutputOutput$$D1S1q1P1Q1P1S SL LSMC1LAC1SMC2LAC2P3S2P3Q3q2P2D2Q2P2（（2）成本递增行业）成本递增行业长期供长期供给曲线给曲线28S2SLP3Q3P3SMC2LAC2OutputOutput$$P1D1S1P1Q1q1SMC1LAC1q2P2D2Q2P2（（3）成本递减行业）成本递减行业29Price($ 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q230 31例题例题132333435例题例题23637例题例题33839例题例题34041例题例题44243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 characterized by pure competition.44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.均衡价格均衡价格均衡产量均衡产量工厂产量工厂产量利润利润4546(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?47(2)解：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 firm’s profit down to zero until there is no incentive for further entry.48(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. 4950(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. 5152例题例题65354例题例题75556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 100.57•(1) If the price 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. 58•(2) If the industry is perfectly competitive will the price remain at $2 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 price below marginal cost, so the price will fall until it reaches $1.50.59•(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 dogs then there are 26 vendors.60•(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 number sold is 2000. If Q=2000 then P=$2, from the demand curve.61•(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 on a per day basis. 62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. 63•(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+tq, or TC+q since t=1. Average cost is now AC+1. Marginal cost is now MC+1.64•(2) What will happen to the firm’s 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 firm’s short-run supply curve 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.65•(3) Will there be entry or exit in the industry ?•If the tax is placed on a single firm, that firm will go out of business. 66。