中级宏观经济学1消费

null现代经济学 Topics on Modern Economics现代经济学 Topics on Modern Economics华南农业大学经济管理学院授课教师授课教师熊启泉 教授、博士生导师 米运生：副教授、北京大学经济博士 正：副教授，在职博士生 喻美辞：讲师、厦门大学经济学博士 课程负责人：熊启泉 Cell phone:13560385018 Email: xqq@scau.edu.cnTextbooksTextbooksHal R. Varian, Intermediate Microeconomics: A Modern Approach (7th Edition), W.W. Norton,2006. Required TextbookTextbooksTextbooks[美] 哈尔·R. 范里安著，《微观经济学: 现代观点》(第六版)，费方域译，上海三联店，上海人民出版社，2006 nullMACROECONOMICS N. Gregory Mankiw6th. ed. 20072009年第六版课程考核课程考核课程性质：本院经管类硕士生学位课 总学时：45学时 学分：2.5学分 上课时间：3—17周（元旦前结束课程） 考试时间：2010年3月 考试不及格：重修（和2010级硕士一起参加考试）null The Theory of Economics does not furnish a body of settled conclusions immediately applicable to policy. It is a method rather than a doctrine, an apparatus of the mind, a technique of thinking which helps its possessor to draw correct conclusions --- John Maynard KeynesIs Economics Useful?Is Economics Useful?A thinking machine Changes the way you view life and understand problems An all round major Jobs for EconomistsJobs for EconomistsBusiness economists Government economists Academic economistsMicroeconomicsMicroeconomicsTheory Applications Labor economics Economics of education Agricultural economics Industrial organizations Health economics ……MacroeconomicsMacroeconomicsTheory Applications Economic growth Economic fluctuations International finance Fiscal policies and monetary policies Open macroeconomics ……Course OutlineCourse OutlineConsumer theory and its applications Producer theory and its applications Game theory and its applications in economic analysis Determination of national income and macroeconomic policies Economic growth theory Risk and uncertainty Asymmetric theory and its applications Market structure analysis Market failure and government interventionLecture 1Lecture 1Consumer theorynull一、预算约束 Budget ConstraintConsumption Choice SetsConsumption Choice SetsA consumption choice set is the collection of all consumption choices available to the consumer. What constrains consumption choice? Budgetary, time and other resource limitations.Budget ConstraintsBudget ConstraintsA consumption bundle containing x1 units of commodity 1, x2 units of commodity 2 and so on up to xn units of commodity n is denoted by the vector (x1, x2, … , xn). Commodity prices are p1, p2, … , pn.Budget ConstraintsBudget ConstraintsQ: When is a consumption bundle (x1, … , xn) affordable at given prices p1, … , pn?Budget ConstraintsBudget ConstraintsQ: When is a bundle (x1, … , xn) affordable at prices p1, … , pn? A: When p1x1 + … + pnxn £ m where m is the consumer’s (disposable) income.Budget ConstraintsBudget ConstraintsThe bundles that are only just affordable form the consumer’s budget constraint. This is the set { (x1,…,xn) | x1 ³ 0, …, xn ³ 0 and p1x1 + … + pnxn = m }. Budget ConstraintsBudget ConstraintsThe consumer’s budget set is the set of all affordable bundles; B(p1, … , pn, m) = { (x1, … , xn) | x1 ³ 0, … , xn ³ 0 and p1x1 + … + pnxn £ m } The budget constraint is the upper boundary of the budget set.Budget Set and Constraint for Two CommoditiesBudget Set and Constraint for Two Commoditiesx2x1Budget constraint is p1x1 + p2x2 = m. m /p1m /p2Budget Set and Constraint for Two CommoditiesBudget Set and Constraint for Two Commoditiesx2x1Budget constraint is p1x1 + p2x2 = m.m /p2m /p1Budget Set and Constraint for Two CommoditiesBudget Set and Constraint for Two Commoditiesx2x1Budget constraint is p1x1 + p2x2 = m.m /p1Just affordablem /p2Budget Set and Constraint for Two CommoditiesBudget Set and Constraint for Two Commoditiesx2x1Budget constraint is p1x1 + p2x2 = m.m /p1Just affordableNot affordablem /p2Budget Set and Constraint for Two CommoditiesBudget Set and Constraint for Two Commoditiesx2x1Budget constraint is p1x1 + p2x2 = m.m /p1AffordableJust affordableNot affordablem /p2Budget Set and Constraint for Two CommoditiesBudget Set and Constraint for Two Commoditiesx2x1Budget constraint is p1x1 + p2x2 = m.m /p1Budget Set the collection of all affordable bundles.m /p2Budget Set and Constraint for Two CommoditiesBudget Set and Constraint for Two Commoditiesx2x1p1x1 + p2x2 = m is x2 = -(p1/p2)x1 + m/p2 so slope is -p1/p2.m /p1Budget Setm /p2Budget ConstraintsBudget ConstraintsFor n = 2 and x1 on the horizontal axis, the constraint’s slope is -p1/p2. What does it mean? Budget ConstraintsBudget ConstraintsFor n = 2 and x1 on the horizontal axis, the constraint’s slope is -p1/p2. What does it mean? Increasing x1 by 1 must reduce x2 by p1/p2.Budget ConstraintsBudget Constraintsx2x1Slope is -p1/p2+1-p1/p2Budget ConstraintsBudget Constraintsx2x1+1-p1/p2Opp. cost of an extra unit of commodity 1 is p1/p2 units foregone of commodity 2.Budget ConstraintsBudget Constraintsx2x1Opp. cost of an extra unit of commodity 1 is p1/p2 units foregone of commodity 2. And the opp. cost of an extra unit of commodity 2 is p2/p1 units foregone of commodity 1. -p2/p1+1How do the budget set and budget constraint change as income m increases?How do the budget set and budget constraint change as income m increases?Original budget setx2x1Higher income gives more choiceHigher income gives more choiceOriginal budget setNew affordable consumption choicesx2x1Original and new budget constraints are parallel (same slope).How do the budget set and budget constraint change as income m decreases?How do the budget set and budget constraint change as income m decreases?Original budget setx2x1How do the budget set and budget constraint change as income m decreases?How do the budget set and budget constraint change as income m decreases?x2x1New, smaller budget setConsumption bundles that are no longer affordable.Old and new constraints are parallel.Budget Constraints - Income ChangesBudget Constraints - Income ChangesIncreases in income m shift the constraint outward in a parallel manner, thereby enlarging the budget set and improving choice.Budget Constraints - Income ChangesBudget Constraints - Income ChangesIncreases in income m shift the constraint outward in a parallel manner, thereby enlarging the budget set and improving choice. Decreases in income m shift the constraint inward in a parallel manner, thereby shrinking the budget set and reducing choice.Budget Constraints - Income ChangesBudget Constraints - Income ChangesNo original choice is lost and new choices are added when income increases, so higher income cannot make a consumer worse off. An income decrease may (typically will) make the consumer worse off.Budget Constraints - Price ChangesBudget Constraints - Price ChangesWhat happens if just one price decreases? Suppose p1 decreases.How do the budget set and budget constraint change as p1 decreases from p1’ to p1”?How do the budget set and budget constraint change as p1 decreases from p1’ to p1”?Original budget setx2x1m/p2m/p1’m/p1”-p1’/p2How do the budget set and budget constraint change as p1 decreases from p1’ to p1”?How do the budget set and budget constraint change as p1 decreases from p1’ to p1”?Original budget setx2x1m/p2m/p1’m/p1”New affordable choices-p1’/p2How do the budget set and budget constraint change as p1 decreases from p1’ to p1”?How do the budget set and budget constraint change as p1 decreases from p1’ to p1”?Original budget setx2x1m/p2m/p1’m/p1”New affordable choicesBudget constraint pivots; slope flattens from -p1’/p2 to -p1”/p2-p1’/p2-p1”/p2Shapes of Budget Constraints with a Quantity PenaltyShapes of Budget Constraints with a Quantity Penaltyx2x1Budget SetBudget Constraint二、偏好二、偏好Preferences nullDescribe preferences Indifference curves Well-behaved preferences Marginal rate of substitution Rationality in EconomicsRationality in Economics Behavioral Postulate: A decisionmaker always chooses its most preferred alternative from its set of available alternatives. So to model choice we must model decisionmakers’ preferences.Preference RelationsPreference RelationsComparing two different consumption bundles, x and y: strict preference: x is more preferred than is y. weak preference: x is as at least as preferred as is y. indifference: x is exactly as preferred as is y.Preference RelationsPreference RelationsStrict preference, weak preference and indifference are all preference relations. Particularly, they are ordinal relations; i.e. they state only the order in which bundles are preferred.Indifference CurvesIndifference CurvesTake a reference bundle x’. The set of all bundles equally preferred to x’ is the indifference curve containing x’; the set of all bundles y ~ x’. Since an indifference “curve” is not always a curve a better name might be an indifference “set”.Indifference CurvesIndifference Curvesx2x1x”x”’x’ ~ x” ~ x”’x’Indifference CurvesIndifference Curvesx2x1z x yppxyzIndifference CurvesIndifference Curvesx2x1xAll bundles in I1 are strictly preferred to all in I2.yzAll bundles in I2 are strictly preferred to all in I3.I1I2I3Indifference CurvesIndifference Curvesx2x1I(x’)xI(x)WP(x), the set of bundles weakly preferred to x.Indifference CurvesIndifference Curvesx2x1WP(x), the set of bundles weakly preferred to x. WP(x) includes I(x).xI(x)Indifference CurvesIndifference Curvesx2x1SP(x), the set of bundles strictly preferred to x, does not include I(x).xI(x)Indifference Curves Cannot Intersect Indifference Curves Cannot Intersect x2x1xyzI1I2From I1, x ~ y. From I2, x ~ z. Therefore y ~ z.Indifference Curves Cannot Intersect Indifference Curves Cannot Intersect x2x1xyzI1I2From I1, x ~ y. From I2, x ~ z. Therefore y ~ z. But from I1 and I2 we see y z, a contradiction.pSlopes of Indifference CurvesSlopes of Indifference CurvesWhen more of a commodity is always preferred, the commodity is a good. If every commodity is a good then indifference curves are negatively sloped.Slopes of Indifference CurvesSlopes of Indifference CurvesBetterWorseGood 2Good 1Two goods a negatively sloped indifference curve.Slopes of Indifference CurvesSlopes of Indifference CurvesIf less of a commodity is always preferred then the commodity is a bad.Slopes of Indifference CurvesSlopes of Indifference CurvesBetterWorseGood 2Bad 1One good and one bad a positively sloped indifference curve.Well-Behaved PreferencesWell-Behaved PreferencesA preference relation is “well-behaved” if it is monotonic and convex. Monotonicity: More of any commodity is always preferred (i.e. no satiation and every commodity is a good).Well-Behaved PreferencesWell-Behaved PreferencesConvexity: Mixtures of bundles are (at least weakly) preferred to the bundles themselves. E.g., the 50-50 mixture of the bundles x and y is z = (0.5)x + (0.5)y. z is at least as preferred as x or y. Well-Behaved Preferences -- Convexity.Well-Behaved Preferences -- Convexity.x2y2x2+y22x1y1x1+y12xyz = x+y2is strictly preferred to both x and y.Well-Behaved Preferences -- Convexity.Well-Behaved Preferences -- Convexity.x2y2x1y1xyz =(tx1+(1-t)y1, tx2+(1-t)y2)is preferred to x and y for all 0 < t < 1.Well-Behaved Preferences -- Convexity.Well-Behaved Preferences -- Convexity.x2y2x1y1xyPreferences are strictly convex when all mixtures z are strictly preferred to their component bundles x and y.zWell-Behaved Preferences -- Weak Convexity.Well-Behaved Preferences -- Weak Convexity.x’y’z’Preferences are weakly convex if at least one mixture z is equally preferred to a component bundle.xzyNon-Convex PreferencesNon-Convex Preferencesx2y2x1y1zBetterThe mixture z is less preferred than x or y.Slopes of Indifference CurvesSlopes of Indifference CurvesThe slope of an indifference curve is its marginal rate-of-substitution (MRS). How can a MRS be calculated?Marginal Rate of SubstitutionMarginal Rate of Substitutionx2x1x’MRS at x’ is the slope of the indifference curve at x’Marginal Rate of SubstitutionMarginal Rate of Substitutionx2x1 MRS at x’ is lim {Dx2/Dx1} Dx1 0 = dx2/dx1 at x’Dx2Dx1x’Marginal Rate of SubstitutionMarginal Rate of Substitutionx2x1dx2dx1dx2 = MRS ´ dx1 so, at x’, MRS is the rate at which the consumer is only just willing to exchange commodity 2 for a small amount of commodity 1.x’MRS & Ind. Curve PropertiesMRS & Ind. Curve PropertiesBetterWorseGood 2Good 1Two goods a negatively sloped indifference curveMRS < 0.MRS & Ind. Curve PropertiesMRS & Ind. Curve PropertiesBetterWorseGood 2Bad 1One good and one bad a positively sloped indifference curveMRS > 0.MRS & Ind. Curve PropertiesMRS & Ind. Curve PropertiesGood 2Good 1MRS = - 5MRS = - 0.5MRS always increases with x1 (becomes less negative) if and only if preferences are strictly convex.MRS & Ind. Curve PropertiesMRS & Ind. Curve Propertiesx1x2MRS = - 0.5MRS = - 5MRS decreases (becomes more negative) as x1 increases nonconvex preferences 三、效用三、效用UtilitynullUtility function (效用函数） Definition Monotonic transformation （单调转换） Examples of utility functions and their indifference curves Marginal utility （边际效用） Marginal rate of substitution 边际替代率 MRS after monotonic transformationUtility FunctionsUtility FunctionsA utility function U(x) represents a preference relation if and only if: x’ x” U(x’) > U(x”) x’ x” U(x’) < U(x”) x’ ~ x” U(x’) = U(x”).ppUtility FunctionsUtility FunctionsUtility is an ordinal (i.e. ordering) concept. [序数效用] E.g. if U(x) = 6 and U(y) = 2 then bundle x is strictly preferred to bundle y. But x is not preferred three times as much as is y.Utility Functions & Indiff. CurvesUtility Functions & Indiff. CurvesConsider the bundles (4,1), (2,3) and (2,2). Suppose (2,3) (4,1) ~ (2,2). Assign to these bundles any numbers that preserve the preference ordering; e.g. U(2,3) = 6 > U(4,1) = U(2,2) = 4. Call these numbers utility levels.pUtility Functions & Indiff. CurvesUtility Functions & Indiff. CurvesAn indifference curve contains equally preferred bundles. Equal preference  same utility level. Therefore, all bundles in an indifference curve have the same utility level.Utility Functions & Indiff. CurvesUtility Functions & Indiff. CurvesSo the bundles (4,1) and (2,2) are in the indiff. curve with utility level U º 4 But the bundle (2,3) is in the indiff. curve with utility level U º 6. On an indifference curve diagram, this preference information looks as follows:Utility Functions & Indiff. CurvesUtility Functions & Indiff. CurvesU º 6U º 4(2,3) (2,2) ~ (4,1)x1x2pUtility Functions & Indiff. CurvesUtility Functions & Indiff. CurvesComparing more bundles will create a larger collection of all indifference curves and a better description of the consumer’s preferences.Utility Functions & Indiff. CurvesUtility Functions & Indiff. CurvesU º 6U º 4U º 2x1x2Utility Functions & Indiff. CurvesUtility Functions & Indiff. CurvesThe collection of all indifference curves for a given preference relation is an indifference map. An indifference map is equivalent to a utility function; each is the other.Utility FunctionsUtility FunctionsThere is no unique utility function representation of a preference relation. Suppose U(x1,x2) = x1x2 represents a preference relation. Again consider the bundles (4,1), (2,3) and (2,2).Utility FunctionsUtility FunctionsU(x1,x2) = x1x2, so U(2,3) = 6 > U(4,1) = U(2,2) = 4; that is, (2,3) (4,1) ~ (2,2).pUtility FunctionsUtility FunctionsU(x1,x2) = x1x2 (2,3) (4,1) ~ (2,2). Define V = U2.pUtility FunctionsUtility FunctionsU(x1,x2) = x1x2 (2,3) (4,1) ~ (2,2). Define V = U2. Then V(x1,x2) = x12x22 and V(2,3) = 36 > V(4,1) = V(2,2) = 16 so again (2,3) (4,1) ~ (2,2). V preserves the same order as U and so represents the same preferences.ppUtility FunctionsUtility FunctionsU(x1,x2) = x1x2 (2,3) (4,1) ~ (2,2). Define W = 2U + 10. pUtility FunctionsUtility FunctionsU(x1,x2) = x1x2 (2,3) (4,1) ~ (2,2). Define W = 2U + 10. Then W(x1,x2) = 2x1x2+10 so W(2,3) = 22 > W(4,1) = W(2,2) = 18. Again, (2,3) (4,1) ~ (2,2). W preserves the same order as U and V and so represents the same preferences.ppUtility Functions: Monotonic TransformationUtility Functions: Monotonic TransformationIf U is a utility function that represents a preference relation and f is a strictly increasing function, then V = f(U) is also a utility function representing . Goods, Bads and NeutralsGoods, Bads and NeutralsA good is a commodity unit which increases utility (gives a more preferred bundle). A bad is a commodity unit which decreases utility (gives a less preferred bundle). A neutral is a commodity unit which does not change utility (gives an equally preferred bundle).Goods, Bads and NeutralsGoods, Bads and NeutralsUtilityWaterx’Units of water are goodsUnits of water are badsAround x’ units, a little extra water is a neutral.Utility functionSome Other Utility Functions and Their Indifference CurvesSome Other Utility Functions and Their Indifference CurvesInstead of U(x1,x2) = x1x2 consider V(x1,x2) = x1 + x2. What do the indifference curves for this “perfect substitution” utility function look like?Perfect Substitution Indifference CurvesPerfect Substitution Indifference Curves55991313x1x2x1 + x2 = 5x1 + x2 = 9x1 + x2 = 13V(x1,x2) = x1 + x2.Perfect Substitution Indifference CurvesPerfect Substitution Indifference Curves55991313x1x2x1 + x2 = 5x1 + x2 = 9x1 + x2 = 13All are linear and parallel.V(x1,x2) = x1 + x2.Some Other Utility Functions and Their Indifference CurvesSome Other Utility Functions and Their Indifference CurvesInstead of U(x1,x2) = x1x2 or V(x1,x2) = x1 + x2, consider W(x1,x2) = min{x1,x2}. What do the indifference curves for this “perfect complementarity” utility function look like?Perfect Complementarity Indifference CurvesPerfect Complementarity Indifference Curvesx2x145omin{x1,x2} = 8358358min{x1,x2} = 5min{x1,x2} = 3W(x1,x2) = min{x1,x2}Perfect Complementarity Indifference CurvesPerfect Complementarity Indifference Curvesx2x145omin{x1,x2} = 8358358min{x1,x2} = 5min{x1,x2} = 3All are right-angled with vertices on a ray from the origin.W(x1,x2) = min{x1,x2}Some Other Utility Functions and Their Indifference CurvesSome Other Utility Functions and Their Indifference CurvesA utility function of the form U(x1,x2) = f(x1) + x2 is linear in just x2 and is called quasi-linear （准线性）. E.g. U(x1,x2) = 2x11/2 + x2.Some Other Utility Functions and Their Indifference CurvesSome Other Utility Functions and Their Indifference CurvesAny utility function of the form U(x1,x2) = x1a x2b with a > 0 and b > 0 is called a Cobb-Douglas utility function. E.g. U(x1,x2) = x11/2 x21/2 (a = b = 1/2) V(x1,x2) = x1 x23 (a = 1, b = 3)Cobb-Douglas Indifference CurvesCobb-Douglas Indifference Curvesx2x1Marginal UtilitiesMarginal UtilitiesMarginal means “incremental”. The marginal utility of commodity i is the rate-of-change of total utility as the quantity of commodity i consumed changes; i.e. Marginal UtilitiesMarginal UtilitiesE.g. if U(x1,x2) = x11/2 x22 thenMarginal UtilitiesMarginal UtilitiesE.g. if U(x1,x2) = x11/2 x22 thenMarginal UtilitiesMarginal UtilitiesE.g. if U(x1,x2) = x11/2 x22 thenMarginal UtilitiesMarginal UtilitiesE.g. if U(x1,x2) = x11/2 x22 thenMarginal UtilitiesMarginal UtilitiesSo, if U(x1,x2) = x11/2 x22 thenMarginal Utilities and Marginal Rates-of-SubstitutionMarginal Utilities and Marginal Rates-of-SubstitutionThe general equation for an indifference curve is U(x1,x2) º k, a constant. Totally differentiating this identity gives Marginal Utilities and Marginal Rates-of-SubstitutionMarginal Utilit