伦敦经济学院高微讲义-一般均衡.ppt

1、Microeconomics,General Equilibrium: price taking,Excess Demand,Decentralis-ation and Trade,A many-person economy,Robinson Crusoes Problem,Excess Demand,Decentralis-ation and Trade,Robinson Crusoes Problem,General Equilibrium,Why price-taking?,A many-person economy,Overview.,So far weve focused on co

2、mpetitive equilibrium analysis. But why? Why concentrate on equilibrium? Why assume competitive behaviour? Lets start by having another look at the exchange economy. Well redraw the Edgeworth box,Some puzzles in competitive equilibrium analysis,General equilibrium,Robinson Crusoes problem,Decentrali

3、- sation and Trade,A many-person Economy,Why price-taking?,Excess demand,The solution concept,Prices and the Core,The solution concept,An exchange economy,Prices and the Core,Why price-taking?,What would I do out of equilibrium? And what would he do?,Lets look at the inner workings.,Building an Edge

4、worth box,x1a,R1a,R2a,x2a,Oa,The situation from Alfs point of view,How Alf responds as p1/p2 changes.,x1a,R1a,R2a,x2a,Oa,Alfs offer curve,What about Bill?,x1b,R1b,R2b,x2b,Ob,The situation from his point of view,.as an Australian,x1b,R1b,R2b,x2b,Ob,How Bill responds as p1/p2 changes.,x1b,R1b,R2b,x2b,

5、Ob,Bills offer curve,The two offer curves,1,x2b,Ob,x1a,x2a,Oa,x1b,R1b,R1a,R2a,R2b,Offers are only consistent where curves intersect,But, by construction.,This is the competitive equilibrium,Satisfies materials balance,E,D,Price-taking utility-maximising Bill,Price-taking utility-maximising Alf,But w

6、hy competitive behaviour? Why should Alf and Bill behave that way? Where do the prices come from?,Given competitive behaviour, the CE is the only consistent allocation,subject to,h h,S pixi M,i=1,U (x ),max,n h h,S pixi M,So where do the prices come from?,We need a more general solution concept Then

7、 examine how price-taking equilibrium relates to this. Lets develop the approach for the exchange economy, though it could apply to more interesting economies.,A fresh approach,General equilibrium,Robinson Crusoes problem,Decentrali- sation and Trade,A many-person Economy,Why price-taking?,Excess de

8、mand,The solution concept,Prices and the Core,An exchange economy,Prices and the Core,An exchange economy,Why price-taking?,View the population.,.as n separate individuals,A coalition.,.is formed by any subgroup,weve got our endowments with us,One day you take your bundle along to the swap shop. .an

9、d some bossy person is there who proposes (insists on?) a particular feasible allocation. You and some others dont like the x bundle you would get under this allocation. .and you find that by using just the resources you all own you could all get a utility level at least as high as that offered to y

10、ou under the proposed allocation. You guys therefore refuse to accept it.,your coalition has blocked the proposed allocation,The idea of blocking: a little story,An allocation is blocked.,.which can do better for itself,if we can find a coalition.,A proposed allocation for the whole economy,.and tha

11、t are feasible,Q 1,2,.,nh,hQ, for some h,A coalition,Bundles that are preferred by members of the coalition.,A formal approach,The Core,is the set of unblocked, feasible allocations,Use the idea of blocking to introduce a basic solution concept,Alf & Bill,Alf,Bill,In a 2-person world there are very

12、few coalitions possible,Use the Edgeworth box.,x2b,Ob,x1a,x2a,Oa,x1b,.to get the contract curve,Alf blocks these allocations.,D,Bill blocks these allocations.,Alf, Bill (together) block these.,Endowment,No-one can block an allocation here,The 2-person core,General equilibrium,Robinson Crusoes proble

13、m,Decentrali- sation and Trade,A many-person Economy,Why price-taking?,Excess demand,The solution concept,Prices and the Core,An exchange economy,The solution concept,An exchange economy,Why price-taking?,x2b,Ob,x1a,x2a,Oa,x1b,D,E,The competitive equilibrium again,x2b,Ob,x1a,x2a,Oa,x1b,D,E,Any compe

14、titive equilibrium must lie in the core,Every CE allocation must belong to the core Of course it is possible that no CE exists (see next lecture) But what of other core allocations which are not CE? Lets take a close-up look,A simple result,D,The extremes of the 2-person core,CE,Remember we are deal

15、ing with a 2-person model,But will there always be non-CE points in the core?,A basic relation.,Alf and his twin brother Arthur have the same preferences and endowments Likewise the twins Bill and Ben Now of course there are more possibilities of forming coalitions,So lets clone the economy,Arthur &

16、 Ben,Arthur,Ben,Alf & Arthur,etc, etc,Bill&Ben,Alf, Arthur &Bill,. plus some new ones,All the old coalitions are possible.,Will these still be core allocations in the 4-person economy?,B,A,Alf n Arthur Bill n Ben,Alf n Arthur Bill n Ben,D,Alf, Arthur,Ben,Bill,G,.leaving the Ben twin outside the coal

17、ition,This allocation is not a solution. But it shows that the core has become smaller,No. Alf-Arthur-Bill can block A.,Alf xa+Ra (G) Arthurxa+Ra (G) Bill xb (A) Ben Rb (D),2Ra + Rb,The coalition, Feasible,How the blocking coalition works,A,B,D,Can this allocation be blocked?,An A-person would be be

18、tter off somewhere here,Bingo!,What if there were 500 of each type.?,If N is bigger there may be more blocking coalitions,A,B,D,E,The only allocation left in the 2N-person core (eventually).,As you clone the economy the core becomes smaller. In the limit it contains only competitive equilibrium allocations. But notice that th