经济学原理-宏观-讲义6

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1、PRINCIPLESOFECONOMICS–MACROECONOMICSWeek6.MacroeconomicEquilibriumandtheIS-LMModelTheEffectsofChangesinAutonomousExpenditureonPandYWehaveseenthat:Ariseinthepricelevel(P)willshifttheaggregateexpenditure(AE)curveupwards;andAnincreaseinautonomousexpenditure(A)independentofpricechangewillshifttheag

2、gregatedemand(AD)curvetotheright.WhatwillbetheeffectsofanincreaseinAonP&Y?TheanswerliesontheshapeoftheSAScurve.Incase(a),anincreaseinAresultsinAE0AE1,andhenceAD0AD1.BecausetheSAS(H)curveishorizontal,YandPremainsunchanged.Incase(b),anincreaseinAresultsinAE0AE1,andhenceAD0AD1.BecausetheSAS(V)curv

3、eisvertical,PandYremainsunchanged.Thereasonisthatthehigherpricelevel,aswehaveseen,reducesAandhenceshiftaggregateexpenditurebacktoAE0.SofarwehavedefinedtheequalityofADandSASasmacroeconomicequilibrium,butwehavesaidlittleaboutthederivationoftheADcurve–thatis,therelationshipbetweenAEandP.Toderiveth

4、eADcurveweneedtotakeintoaccounttheconditionsofdemandandsupplyinboththegoodsmarketandthemoneymarket.TheIS-LMmodelthatwenowturnisanessentialtoolforthispurpose.5FlowEquilibrium:TheISCurveRecalltheaggregateplannedexpenditureequationAE=C+I+G+(EX-IM)=(a+I+G+EX)+[b(1–t)–m]Y=A+YPreviouslywesaidthatN(=Y

5、)isinducedexpenditurebecauseitvarieswithY.NowconsiderA,theautonomousexpenditure,whoseinvestmentcomponentisinfactaffectedbytherealinterestrate,i.e.,I=c–di.(similartotheconsumptionfunctionC=a+bYd).TheaggregateexpenditureequationthusbecomesAE=(a+c+G+EX)–di+[b(1–t)–m]Y=(A*–di)+Y(A=A*–di)Wenowreform

6、ulatetheconditionfortheequalityofAEandY–knownasflowequilibrium–totakeintoaccounttheinfluenceofthechangeininterestrate(whichisdeterminedbyI=S).TheIScurveshowscombinationsofrealGDP(Y)andtheinterestrate(i)atwhichaggregateplannedexpenditureequalsY.PointsontheIScurvearepointsatwhichplannedinjectioni

7、ntothecircularflowofexpenditureandincomeequaltheplannedleakagesfromthecircularflow.Inaneconomywithnogovernmentandnoforeignsector,alongtheIScurveplannedinvestmentequalssaving.5ShiftsintheIScurve:notethatanincreaseinautonomousexpend