电子科技大学：《高级宏观经济学 Advanced Macroeconomics》课程教学资源（课件讲稿）Lecture 03a Ramsey Model

Technology and Constraints Time constraint:+=1 Resource constraint:c,+i,<y Neoclassical technology y,=F(k,)=1f(K),K,=k,/1 Change in capital k+1=(1-δ)k,+i, →C,+k+1≤F(k,l)+(1-δ)k, 电子科大经管学院马捷 6

Technology and Constraints  Time constraint:  Resource constraint:  Neoclassical technology  Change in capital 电子科大经管学院 马捷 6 z t  l t  z  1 t t t c  i  y t t t t t t t t y  F ( k ,l )  l f ( ),   k / l t t t k   k  i  ( 1 ) 1  t t t t t c k F ( k , l ) ( 1 ) k    1    

The Ramsey Problem Choose maxU=∑B'U(c,l-l,) t=0 s.t.C,+k+1≤F(k,l)+(1-6)k,t≥0， C,k+1≥0,1，∈[0,1] ko>0 is given. 电子科大经管学院马捷

The Ramsey Problem 电子科大经管学院 马捷 7   0 . , 0, [ 0,1], . . ( , ) ( 1 ) , 0, max ( ,1 ) Choose , 0 1 1 0 0 1 0 k is given c k l s t c k F k l k t U U c l c ,l ,k t t t t t t t t t t t t t t t t                     

Optimal Control ·The Lagrangian: 00 L,=∑B'U(c,1-l,)+∑4，[F(k,l,)+(1-6)k,-C,-k+] t=0 t=0 Let=u,B'and define Hamiltonian as: H,=H(k,k+1,C,,) 三U(c,1-1,)+,[F(k,l)+(1-δ)k,-C,-k+]→ L。=∑B{U(c,1-1,)+,[F(k,)+(1-6)k,-c,-k+1]} 1=0 00 ∑BH,orL,=H,+L4l t=0 电子科大经管学院马捷 8

Optimal Control  The Lagrangian: 电子科大经管学院 马捷 8               0 1 0 0 ( ,1 ) [ ( , ) ( 1 ) ] t t t t t t t t t t t L  U c l  F k l  k c k   1 0 0 0 1 1 1 ( ,1 ) [ ( , ) ( 1 ) ] ( ,1 ) [ ( , ) ( 1 ) ] ( , , , , ) Let / :                               t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t H or H U c l F k l k c k U c l F k l k c k H H k k c l and define Hamiltonia n as L L L           

FOCs H,≥0宁 0c 0c. H,=0⊙U,(C,2)=元 Oc. al, aH,=0户 al, =0台U(c,)=,F(k,) al, → aLo=β L=0 k ak+1 =0台-A+Bk 台=[1-δ+Fx(k+1,+)]2+1 U(C,2,)/U(C,2,)=F(k,,) U.(C,)[BU.(c41,41)】=1-6+Fx(k+,l4) 电子科大经管学院马捷 9

FOCs 电子科大经管学院 马捷 9                                                                   ( , )/ ( , ) 1 ( , ) ( , )/ ( , ) ( , ) [1 ( , )] 0 0 0 0 ( , ) ( , ) 0 0 ( , ) 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 c t t c t t K t t z t t c t t L t t t K t t t t t t t t t t t t z t t t L t t t t t t t t c t t t t t t t t t U c z U c z F k l U c z U c z F k l F k l k H k H k H k U c z F k l l H l H l U c z c H c H c               L L L

Kuhn-Tucker condition Suppose for a moment that the horizon was finite,T<o. L 8kT =BT L≥0amdk1≥0，p HTk=0 KT+ →47=B7≥0andk7+1≥0，with B",2k+1=0 →either k+1=0orB,=0 IfT=∞，limB,k+1=limB'Uc(c,2,)k+1=0 电子科大经管学院马捷 10

Kuhn-Tucker condition  Suppose for a moment that the horizon was finite, T< ∞.  If T= ∞, 电子科大经管学院 马捷 10 0 0 0 0, 0 0 0, 0 1 1 1 1 1 1 1 1                           T T T T T T T T T T T T T T T T T T T either k or and k with k k k H and k k H k          L lim lim ( , ) 0 1  1       c t t t t t t t t t   k  U c z k