2
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339
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Cass[3] Koopmans[4] Ramsey[5] , ("#"KÆ,, ’1 ($K*1,
Solow !#(-0, !G RCK ! Ramsey !. ("#"KÆ,K,
Samuelson[6] 8 % !K9Æ,, ! (saddle) 10<=, !)’L
4M)’. Ramsey ! L8 Solow !I4, -JD1#B
-.
0-B-0, M%">. Arrow[7] C (learning by
doing) !, 0 B M , 8*!8 Æ,, B%
AK !8. Uzawa[8] )*M! ?N!, !
M . Romer[9,10] Lucas[11,12] ??/ !!-, $0 I
#, ),N%JB, K$0 ! , ,
?.9 Arrow-Romer ! Uzawa-Lucas !.
2.2 !"# !r1
Ramsey !Æ’"#"’1$", C’1$8, (infinite horizon), B(%
93 16, 932P%Æ,. Samuelson[13] Diamond[14]
8"#"’1$8, Æ,, (, 0 "#"’1$3, ?$, ?#Q
, (K’1, ?=1)C)* OLG !. 0#
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, )-. #, OLG !, * ".
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, C!"
340
38
’1, % $C!", C!! , "4/$.
2% Futagami Nakajima[21] @?:,/$0 98>*/%’1(,
’, /%0 , m, % t Q, 0 m /%, 0 #Q/%^ , m #Q/%
9 <. &!, %R N, 5, 0 m 8 C,
[-\ N/m. /%, d, /% 0 d 8C!", 6"S,
%’1(, d m 8, ’10X(! N7 . $ Æ C
, %"3 L = dN/m, 3 O = (m − d)N/m. S-8 E, %,
/% /% <, <, ]’=*)’.
/! Æ5 (1) @Q*+ :
(1)
B(x, t) #QQ x /% t Q/!, C(x, t) #QQ x /% t Q’13, r(t)
#Q t Q -, W (x, t) #Q t Q4!. /%#F, 4!J:
˙B(x, t) = W (x, t) + r(t)B(x, t) − C(x, t)
W (x, t) =
W (t), x ≤ t ≤ x + d
0,
x + d < t ≤ x + m
/% -,/!, P,G>, J5 (3):
B(x, x) = B(x, x + m) = 0
’P[,"/! b(x, t) = B(x, t)/A(t), /!*+ I V.5:
˙b(x, t) + b(x, t)g = ω(x, t) + r(t)b(x, t) − c(x, t)
, P[,"/! Æ5 (5)∼(7) ?:*+ :
˙b(x, t) = ω(x, t) + (r(t) − g)b(x, t) − c(x, t)
ω(x, t) =
ω(t), x ≤ t ≤ x + d
0,
x + d < t ≤ x + m
b(x, x) = b(x, x + m) = 0
/%\%82% CRRA !, -%.5:
u(C(x, t)) = C(x, t)(1−θ)
1 − θ
, θ > 0
θ #Q_]6, θ JK, ’1W@(D4%BJ], /%JLR^’1>$8
. Q x /% %:
C(x, t) = A(t)c(x, t), A(t) = A(0)egt :
x+m
e
x
−ρ(t−x) C(x, t)(1−θ)
1 − θ
Q x /%#F, A(0)1−θeρx R, */:
max
x+m
e
x
−ρ(t−x) C(x, t)(1−θ)
dt
1 − θ
x+m
e
x
dt = A(0)1−θeρx
−(ρ−g(1−θ))t c(x, t)(1−θ)
1 − θ
dt
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
⎧⎪⎪⎪⎪⎪⎪⎪⎪⎨
⎪⎪⎪⎪⎪⎪⎪⎪⎩
s.t.
x+m
−(ρ−g(1−θ))t c(x, t)(1−θ)
x
e
max
˙b(x, t) = ω(x, t) + (r(t) − g)b(x, t) − c(x, t)
ω(x, t) =
1 − θ
ω(t), x ≤ t ≤ x + d
0,
x + d < t ≤ x + m
dt
b(x, x) = b(x, x + m) = 0
’ Hamilton 8 H = e−(ρ−g(1−θ))t c(x,t)(1−θ)
1−θ + λ[ω(x, t) + (r(t) − g)b(x, t) − c(x, t)], :
= r(t) − ρ − θg
˙c(x, t)
c(x, t)
θ
$ :
c(x, t) = c(x, x)eP (x,t)
Æ, f
7<, lim
k→0
(k) > 0, f
(k) = ∞,
f
(k) = 0.
lim
k→∞ f
-! D4 , :
P[,"! #Q:
3.3 / 0C
% %’1!, :
r(t) = f
(k(t))
ω(t) = f(k(t)) − k(t)f
(k(t))
(19)
(20)
341
(14)
(15)
(16)
(17)
(22)
(23)
∗
(24)
(25)
, :
2
7, P (x, v) =
θ
v
x
r(t)−ρ−θg
dt. #, ’ R(x, v) =
x (r(t) − g)dt.
5 (5) ?DW e−R(x,t) Q x B x + m :
−R(x,v)dv −
$ b(x, x) = b(x, x + m) = 0, c(x, t) = c(x, x)eP (x,t), :
−R(x,v)|x+m
b(x, v)e
ω(v)e
x+d
=
x
x
x
v
x+m
c(x, v)e
−R(x,v)dv
0 =
ω(v)e
x+d
x
−R(x,v)dv −
x+d
x
x+m
x
c(x, x) =
x+m
c(x, x)eP (x,v)−R(x,v)dv
x
ω(v)e−R(x,v)dv
eP (x,v)−R(x,v)dv
c(x, t) =
x+d
x
x+m
x
ω(v)e−R(x,v)dv
eP (x,v)−R(x,v)dv
eP (x,t)
#5?:/% $0[QP[,/’1, 5
ω(v)e−R(x,v)dv 4"#/
% 3U, /%7%, 931a’1, 2 @$Æ4_.
3.2 A.-
x+d
x
8/: Y (t)! K(t)" L(t) B A(t), 83S8 t 8, 7-%.5:
(18)
(k) < 0, , f(0) = 0. #, V.58 f J Inada
Y (t) = F (K(t), A(t)L(t))
(21)
7, ˜c(t) #Q t Q%@,/%P[,/’1!, A(t) ˜c(t) #Q t Q%@,
/%4’1!. I V.5, P[,"! 3+ :
˙K(t) = F (K(t), A(t)L(t)) − A(t)˜c(t)
˙k(t) = f(k) − ˜c(t)
L(t)
− k(t)g
)!, ˙k(t) 4!LA1!, 4! f(k) − ˜c(t)
L(t), Æ,, DZ, 1
! k(t)g. $\R N/m, x Q @,/% t QP[,/’1!
N/m · c(x, t). t Q, %/% Q t − m, /% Q t, t Q
%@,/%P[,/’1!:
N
m
c(x, x)eP (x,t)dx
c(x, t)dx =
˜c(t) =
N
m
t
t−m
t
t−m
)* ˙k = 0, k R, #, - r P[,"! ω R, 8 t , r
∗, 5 (23) I:
ω
˜c(t) = N
m
· ω
∗
∗( r
θ
− ρ
(e( r∗
θ
θ
− r
− ρ
∗)d − 1)(e( r
∗−ρ−θg
∗)(e(g−r
−r∗)m − 1)(g − r∗)( r∗−ρ−θg
)m − 1)
)
θ
θ
θ
$ L = dN
m , :
˜c(t)
L(t)
∗
= ω
d
∗
· ( r
θ
− ρ
(e( r∗
θ
θ
− r
− ρ
θ
∗)d − 1)(e( r
∗)(e(g−r
−r∗)m − 1)(g − r∗)( r∗−ρ−θg
∗−ρ−θg
θ
)
)m − 1)
θ
342
38
)* ˙k = 0, "5 (22) :
− ρ
(26)
(e( r∗
∗), 72@ {ρ, θ, d, m, g} #"’. ]’
∗)(e(g−r
−r∗)m − 1)(g − r∗)( r∗−ρ−θg
) − ω
d
∗) − k
f(k
∗ = f(k
∗)d − 1)(e( r
)m − 1)
− r
− ρ
∗ = f
∗), ω
∗−ρ−θg
· ( r
(k
(k
= k
∗
∗
∗
∗
g
)
∗
θ
θ
θ
θ
θ
θ
5, r
C., (=@, 0.
3.4 !1EF34
f
=/8D1 - <-8. ?:&!, B(% Æ
C, - <-*]’, #%*]’=*)’,
. )K 1949–1957 8, ’ (1C
:O ‘7<, <-[B, -4 :(1, # /-:
:>*. 1949 , 5.42 , 1957 , 6.47 , 8 8\! 1.05 , 9
)K>C:b. ), =8$ “ 7” “ <7” c1’.
J(0)
%b 3QQ “ 7” , %$0 QQ “ <7” , ?$
A%%=. -%, 62%Æ,, ’b 3
˙J(t)
J(t) = n 1’. n #Q-, B( n > 0, a-b 3!; B
J, 78$5
( n < 0, a-b 3L. cZC, !R 3
6 “7” , ! n < 0, 4, ! @, n > 0 P
%. Æ,Q 3 J(0), # t Q 3 #Q J(t) = J(0)ent. t
Q, % 0 m , Q t t−m, Q x \ J(0)enx, ,
˙N (t)
% N(t) =
N (t) =
(nent−nen(t−m))
(ent−en(t−m)) = n. t Q, %" 0 d , Q t t−d, Q
n (ent − en(t−d)).
x \ J(0)enx, , %"3 L(t) =
(nent−nen(t−d))
(ent−en(t−d)) = n. , %
%"-#Q
(nen(t−d)−nen(t−m))
n (en(t−d) − en(t−m))
3-#Q O(t) =
(en(t−d)−en(t−m)) = n.
(ent−en(t−d))
(ent−en(t−m)) = 1−e−nd
$ , %"] L(t)
N (t) = l(t) =
N (t) =
1 − o(t), l(t) #Q"], o(t) #Q] -, l(t) o(t)
8 t , I l o. %-$0 Bd=, ∂l
∂n =
de−nd(1−e−nm)−me−nm(1−e−nd )
> 0, $ ^, "’$0 , B(3L]’ 8, #
n (ent − en(t−m)). %-#Q
t−d
t−m J(0)enxdx = J(0)
t−d J(0)enxdx = J(0)
t−m J(0)enxdx = J(0)
1−e−nm . ’ L(t)
˙L(t)
L(t) =
˙O(t)
O(t) =
n
J(0)
n
J(0)
n
J(0)
n
J(0)
J(0)
J(0)
J(0)
n
n
n
n
t
t
(1−e−nm)2
=; 3,3!L, =. ∂l
0, $ ^, $0 J, "J, JR.
3.5 !56H/ 0C
∂m = n(e−nd−1)e−nm
(1−e−nm)2 <
]’ C7<&!%L, /\@7<]
0, #)*6I!. x Q /%#F, 7 ’1*de/ %5 (16)
5 (17) ?:. x Q /%3 J(x) = J(0)enx, x Q @,/% t QP[,/
’1! J(0)enxc(x, t). t Q, %/% Q t − m, /% Q
t, t Q%@,/%P[,/’1!:
t
t−m
t
t−m
˜c(t) =
J(x)c(x, t)dx =
J(0)enxc(x, t)dx
% %’1!, :
˙K(t) = F (K(t), A(t)L(t)) − A(t)˜c(t)
, P[,"! 3+ :
˙k(t) = f(k) − ˜c(t)
L(t)
− k(t)(g + n)
(27)
(28)
(29)
2
, :
)!, ˙k(t) 4!LA1!, 4! f(k) − ˜c(t)
L(t), Æ,, DZ, 1
! k(t)(g + n). )* ˙k = 0, k R, #, - r P[,"! ω R, 8 t
, r
ω
343
∗
θ
∗
ω
c(x, x) =
∗)(e(g−r
∗, c(x, x)c(x, t)˜c(t) I:
∗( r
(e( r∗
∗)d − 1)
− r
−r∗)m − 1)(g − r∗)
∗−ρ−θg
− r
∗)(e(g−r
θ
−r∗)m − 1)(g − r∗)( r∗−ρ−θg
− ρ
− r
∗)d − 1)
−r∗)m − 1)(g − r∗)
· e( r
− ρ
θ
− ρ
∗)(e(g−r
∗)d − 1)(e( r
− ρ
(e( r∗
∗( r
(e( r∗
− ρ
θ
− ρ
c(x, t) =
)(t−x)
∗−ρ−θg
∗( r
ω
∗
∗
θ
θ
θ
θ
θ
θ
θ
θ
θ
θ
θ
(30)
(31)
(32)
−n)m − 1)
− n)
˜c(t) =
J(0)enxc(x, t)dx = J(0)ent · ω
t
t−m
n (ent − en(t−d)), :
, L(t) = J(0)
∗)d−1)(e( r
∗
− ρ
−r
∗( r
(e( r∗
θ
− ρ
θ
θ
n (ent − en(t−d))
J(0)
∗−ρ−θg
∗)(e(g−r
−r∗)m−1)(g−r∗)( r∗−ρ−θg
J(0)ent · ω
=
θ
θ
θ
˜c(t)
L(t)
−n)m−1)
−n)
∗( r
ω
(e( r∗
∗
− r
∗)(e(g−r
− ρ
∗)d − 1)(e( r
θ
−r∗)m − 1)(g − r∗)( r∗−ρ−θg
− ρ
θ
θ
θ
∗−ρ−θg
θ
−n)m − 1)n
− n)(1 − e−nd)
=
θ
(33)
, $P[,"! 3+ :
θ
θ
θ
θ
∗
f
∗
∗
∗−ρ−θg
(k
(k
− r
∗ = f
∗( r
) − ω
(e( r∗
∗ = f(k
−n)m − 1)n
− n)(1 − e−nd)
∗)(e(g−r
− ρ
∗)d − 1)(e( r
θ
−r∗)m − 1)(g − r∗)( r∗−ρ−θg
− ρ
∗) − k
∗
f(k
∗), ω
(34)
∗), 72@ {ρ, θ, d, m, n, g} #"’. 5, J
5, r
∗) = g + n, (" (, , 7c (^:)*., C%
(k
f
(, Æ,8_ - e.F!, (-%^). "’@‘, %
(+Æ P[,"! 3 5 (34), k1 k2 ?/ 0. B 1 @Q, g k1
)’, k2 )’, -%, ! + 5 (29), k k2 -R"KKE, ˙k(t) < 0, #
k k2; k k2 -"KKE, ˙k(t) > 0, # k k2. , k2 )’,
, k1 )’. %10<=P[,"! 3 k2.
(g + n)
= k
θ
k1
k2
=0.6 n=-0.0123 g=0.05
k
=0.01 =0.75 d=37 m=48
=0.01 =0.75 d=37 m=56
=0.01 =0.75 d=37 m=70
7 1 K89:; sM<
7 2 K89:; sM