北大微观经济学课件]ch9BuyingandSelling

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1、ChapterNineBuyingandSelling购买和销售StructureEndowments（禀赋）BudgetconstraintswithendowmentsNetdemandsPriceoffercurveExample:LaborsupplyComparativestaticsSlutskyequationrevisitedBuyingandSellingTradeinvolvesexchange--whensomethingisboughtsomethingelsemustbesold.Whatwillbebought?Whatwillbesold?Who

2、willbeabuyer?Whowillbeaseller?BuyingandSellingAndhowareincomesgenerated?Howdoesthevalueofincomedependuponcommodityprices?Howcanweputallthistogethertoexplainbetterhowpricechangesaffectdemands?EndowmentsThelistofresourceunitswithwhichaconsumerstartsishisendowment（禀赋）.Aconsumer’sendowmentwillb

3、edenotedbythevector(omega).EndowmentsE.g.statesthattheconsumerisendowedwith10unitsofgood1and2unitsofgood2.Whatistheendowment’svalue?Forwhichconsumptionbundlesmayitbeexchanged?Endowmentsp1=2andp2=3sothevalueoftheendowmentisQ:Forwhichconsumptionbundlesmaytheendowmentbeexchanged?A:Foranybundl

4、ecostingnomorethantheendowment’svalue.BudgetConstraintsRevisitedSo,givenp1andp2,thebudgetconstraintforaconsumerwithanendowmentisThebudgetsetisBudgetConstraintsRevisitedx2x1w1w2BudgetConstraintsRevisitedx2x1w1w2BudgetsetChangingEndowmentsx2x1(w1’,w2’)(w1”,w2”)(w1,w2)ChangingtheendowmentChang

5、ingPricesx2x1w1w2ChangingpricesoftheendowmentChangingPricesx2x1w1w2BudgetsetChangingPricesx2x1w1w2Theendowmentpointisalwaysonthebudgetconstraint.Sopricechangespivottheconstraintabouttheendowmentpoint.NetDemandTheconstraintisThatis,thesumofthevaluesofaconsumer’snetdemands（净需求）iszero.Ne

6、tDemandsSupposeandp1=2,p2=3.ThentheconstraintisIftheconsumergrossdemands(毛需求）(x1*,x2*)=(7,4),then3good1unitsexchangefor2good2units.Netdemandsarex1*-w1=7-10=-3andx2*-w2=4-2=+2.NetDemandsp1=2,p2=3,x1*-w1=-3andx2*-w2=+2soThepurchaseof2extragood2unitsat$3eachisfundedbygivingup3good1unitsat$

7、2each.NetDemandsatDifferentPricesx2x1w1w2x2*x1*Atprices(p1,p2)theconsumersellsunitsofgood1toacquiremoreunitsofgood2.Netsellerofgood1x2x1w1w2x2*x1*Atprices(p1’,p2’)theconsumersellsunitsofgood2toacquiremoreofgood1.Netbuyerofgood1NetDemandsatDifferentPr