竞争市场利润最大化与均衡中央财经大学张苏.ppt

1,假设：厂商追求利润最大化,不符合三条件,定义：完全竞争市场,分析框架：,结论 短期供给线；三种长期供给线,经验研究,符合三条件,竞争市场利润最大化与均衡,短期均衡：短期供给线、生产者剩余,长期均衡：长期供给线,长期利润最大化受冲击：税收效应,2,1.1厂商追求利润最大化的假设,3,2.1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 （ Product homogeneity）； （2）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 （ Free entry and exit ）,4,Industry,（1）产品同质：存在市场均衡价格P,5,Firm（个别公司）,Industry(整个产业）,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。,6,Firm,AVCi,AVCj,市场均价P=4,7,Firm,2.2完全竞争市场的重要性质,8,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,9,3.1.分析框架：数学解,（q）：利润,利润取到极大值的三个数学条件,10,A,q1 : MR MC q2: MC MR q*: MC = MR,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,11,MC,AVC,AC,A,4.1.短期均衡MR=MC,情形1：利润为正,12,MC,AVC,AC,A,情形2：利润为0,A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）,B,13,当MRMC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MRMC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。,14,MC,AVC,AC,A,情形3：弥补全部可变成本之外还能弥补部分固定成本,ACAVC=固定成本,固定成本,可变成本,15,MC,AVC,AC,A,情形4：刚好弥补全部可变成本，不能弥补一点固定成本,16,MC,AVC,AC,A,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,17,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。,18,Price ($ per unit),Output,MC,4.2.1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,19,4.2.2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,20,Price ($ per unit of output),Output,4.3.1由短期条件理解生产者剩余的定义：几何,C,D,21,4.3.2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,经济利润,23,Price ($ per unit of output),Output,市场的生产者剩余,24,Price,Output,LAC,LMC,4.4.1从长期利润最大化到长期均衡,25,Price,Output,LAC,LMC,4.4.2从长期利润最大化到长期均衡,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,A,A点为长期均衡点，共有5条线经过该店,26,4.5行业的长期供给曲线,27,Output,Output,$,$,SL,（1）成本不变行业,28,Output,Output,$,$,（2）成本递增行业,长期供给曲线,29,Output,Output,$,$,（3）成本递减行业,30,Price ($ per unit of output),Output,t,MC2 = MC1 + tax,AVC2,4.5长期利润最大化受到税收冲击的情形,q2,31,32,例题1,33,34,35,36,例题2,37,38,例题3,39,40,例题3,41,42,例题4,43,44,例题5,Suppose 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.,45,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 均衡产量 工厂产量 利润,46,47,(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?,48,(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 firms profit down to zero until there is no incentive for further entry.,49,(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.,50,51,(4) 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.,52,53,例题6,54,55,例题7,56,57,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.,58,(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.,59,(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.,60,(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.,61,(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.,62,(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.,63,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.,64,(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.,65,(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 is its marginal cost curve above average