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1、竞争市场上的企业什么是竞争市场?l完全竞争市场 perfectly competitive market 具备以下特点： 市场有许多买者和卖者. 各个卖者提供的物品大体上是相同的. 企业可以自由地进入或退出市场.什么是竞争市场?l由于以上条件： 市场上任何一个买者或卖者的行为对市场价格 的影响都可以忽略不计. 每一个买者和卖者都必须接受市场决定的价格 （价格接受者）. 什么是竞争市场? l竞争市场：有许多交易相同产品的买者和 卖者，以至于每一个买者和卖者都是价格 的接受者.竞争企业的收益l总收益 TR = (P Q)竞争企业的收益l总收益与产量同比例变动（价格给定）.竞争企业的收益l平均收益A
2、verage revenue 告诉我们企业从 销售的普通一单位中得到了多少收益.l平均收益是总收益除以产量.竞争企业的收益l对所有企业，平均收益等于物品的价格.竞争企业的收益l边际收益Marginal revenue 每多销售一单 位产量所引起的总收益变动量. MR =TR/ Ql对竞争企业来说，边际收益等于物品的价 格。Table 1 Total, Average, and Marginal Revenue for a Competitive FirmCopyright2004 South-Western利润最大化与竞争企业的供给曲线l竞争企业的目标是利润最大化.l这意味着企业需要寻找到使总
3、收益和总成 本之差最大化的那个产量.Table 2 Profit Maximization: A Numerical ExampleCopyright2004 South-WesternFigure 1 Profit Maximization for a Competitive FirmCopyright 2004 South-WesternQuantity0Costs and RevenueMCATCAVCMC1Q1MC2Q2通过生产边际成本等于边际收益的产量企业使利润最大化QMAXP = MR1 = MR2 P = AR = MR利润最大化与竞争企业的供给曲线lMR MC ，增加 QlMR
4、 AVC, firm will continue to produce in the short run.If P ATC, the firm will continue to produce at a profit.企业的短期停止营业决策l竞争企业的短期供给曲线short-run supply curve是平均可变成本（AVC）以上的边际 成本曲线（MC）.企业进入或退出一个市场的长期决策l在长期，如果从生产中得到的收益将小于 它的总成本，企业就退出. 如果TR TC,进入 如果TR/Q TC/Q，进入 如果P ATC，进入. Figure 4 The Competitive Firms L
5、ong-Run Supply CurveCopyright 2004 South-WesternMC = long-run SFirm exits if P ATC 竞争市场的供给曲线l竞争市场的长期供给曲线是边际成本曲线 位于平均总成本曲线之上的那一部分.Figure 4 The Competitive Firms Long-Run Supply CurveCopyright 2004 South-WesternMCQuantityATC0CostsFirms long-run supply curve竞争市场的供给曲线l短期供给曲线 平均可变成本之上的边际成本曲线.l长期供给曲线 边际成本
6、曲线位于平均总成本曲线最低点以上 的部分.用竞争企业图形来衡量利润l利润=TR-TCl利润=(TR/Q-TC/Q) Ql利润=(P-ATC) QFigure 5 Profit as the Area between Price and Average Total CostCopyright 2004 South-Western(a) A Firm with ProfitsQuantity0PriceP = AR = MRATCMCPATCQ (profit-maximizing quantity)ProfitFigure 5 Profit as the Area between Price a
7、nd Average Total CostCopyright 2004 South-Western(b) A Firm with LossesQuantity0PriceATCMC(loss-minimizing quantity)P = AR = MRPATCQLoss竞争市场的供给曲线l市场供给曲线是每个企业供给曲线的加总. 短期：有固定数量企业的市场l假设企业相同l在任意一种价格时，每个企业供给使边际 成本等于价格的产量. l市场供给曲线反映了个别企业的边际成本 曲线. Figure 6 Market Supply with a Fixed Number of FirmsCopyrigh
8、t 2004 South-Western(a) Individual Firm SupplyQuantity (firm)0PriceMC1.00100$2.00200(b) Market SupplyQuantity (market)0PriceSupply1.00100,000$2.00200,000长期：有进入与退出的市场供给l假设技术相同，市场相同，因此成本曲线 相同l在利润变为零之前，企业将进入或退出市 场l.长期：有进入与退出的市场供给l在这种进入和退出过程结束时，仍然留在 市场中的企业经济利润必为零.l只有当价格与平均总成本被推向相等时， 进入与退出过程才结束.l有自由进入与退出
9、时，竞争市场长期均衡 一定是企业在其有效规模时运行.Figure 7 Market Supply with Entry and ExitCopyright 2004 South-Western(a) Firms Zero-Profit ConditionQuantity (firm)0Price(b) Market SupplyQuantity (market)Price0P = minimum ATCSupplyMCATCl在长期，价格等于最低平均总成本l长期市场供给曲线是这种价格时的水平线竞争企业获得零利润仍旧经营的原因l利润等于总收益减总成本.l总成本包括企业的所有机会成本.l在零利润均
10、衡时，企业的收益补偿了所有 者期望用于使其企业维持的时间和金钱.短期与长期的需求移动l短期内，需求增加使价格和产量上升.l由于价格高于平均总成本，企业赚得正利 润.l长期，市场利润鼓励新企业进入，供给增 加使价格下回到最低平均总成本，利润为 零，企业停止进入，市场达到长期均衡l长期，价格不变，企业数量和总供给量增 加Figure 8短期与长期的需求移动Firm(a) Initial ConditionQuantity (firm)0PriceMarketQuantity (market)Price0DDemand, 1SShort-run supply, 1P1ATCLong-run supp
11、lyP11QAMCFigure 8短期与长期的需求移动Copyright 2004 South-WesternMarketFirm(b) Short-Run ResponseQuantity (firm)0PriceMCATCProfitP1Quantity (market)Long-run supplyPrice0D1D2P1S1P2Q1AQ2P2BFigure 8短期与长期的需求移动Copyright 2004 South-WesternP1Firm(c) Long-Run ResponseQuantity (firm)0PriceMCATCMarketQuantity (market)P
12、rice0P1P2Q1Q2Long-run supplyBD1D2S1AS2Q3C长期供给曲线向右上方倾斜的原因l用于生产的资源数量可能是有限的.l企业可能有不同成本.长期供给曲线向右上方倾斜的原因l边际企业 边际企业marginal firm是如果价格有任何下降 就退出市场的企业.长期供给曲线向右上方倾斜的原因l由于企业在长期中比在短期中更容易进入 和退出，所以长期供给曲线一般比短期供 给曲线更富有弹性SummarylBecause a competitive firm is a price taker, its revenue is proportional to the amount o
13、f output it produces.lThe price of the good equals both the firms average revenue and its marginal revenue.SummarylTo maximize profit, a firm chooses the quantity of output such that marginal revenue equals marginal cost. lThis is also the quantity at which price equals marginal cost.lTherefore, the
14、 firms marginal cost curve is its supply curve.SummarylIn the short run, when a firm cannot recover its fixed costs, the firm will choose to shut down temporarily if the price of the good is less than average variable cost.lIn the long run, when the firm can recover both fixed and variable costs, it
15、 will choose to exit if the price is less than average total cost.SummarylIn a market with free entry and exit, profits are driven to zero in the long run and all firms produce at the efficient scale.lChanges in demand have different effects over different time horizons.lIn the long run, the number of firms adjusts to drive the market back to the zero-profit equilibrium.
