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Advanced Modern MacroeconomicsExogenous Growth
Max Gillman
University of Missouri-St. Louis
10 October 2016
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 1 / 49
Chapter 11: Exogenous GrowthChapter Summary
Exogenous technological progress in goods sectorOutput growth rate a simple function of productivity growth.Account for basic facts about the growth process.
Modi�cation to consumption demand and AS � AD.Interest rate no longer simple sum
of time preference rate and depreciation rate;interest rate still function of exogenous parametersbecause of exogeneous growth rate.
Calibration two percent targeted growth rate.Same interest rate and wage rate as beforeif time preference rate is lowered.
Goods, Labor growth shown over 4 periods.Trend downwards in time endowment
captures trend upwards in education time.and trend downwards in labor hours per week.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 2 / 49
Building on the Last Chapters
Parts 2, 3, 4 allow technology progress
in terms of increase in output productivity parameter.Dynamic Part 4 assumes zero exogenous growth.
Now exogenous growth rate is positive instead of zero
through continuous increase in output productivity.
Calibration is shown with same interest rate
by having lower rate of time preference.
Goods productivity factor increases at constant rate over time;
standard neoclassical growth model.
Adds time endowment decrease at small rate over time.
Two comparative statics explain trends in growth facts, employment.
Still consistent with �uctuations around trends for business cycle.Growth theory with trends in parameters consistentwith business cycle theory of changes in parameters.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 3 / 49
Learning Objective
Baseline dynamic model can have positive exogenous growth.
Focus on intertemporal marginal rate of substitution.
How interest rate is determined once growth rate is given.
Then revise AS � AD framework.
Graphical changes of AS � AD as in growth facts.
Use same comparative static tools:
goods and time endowment changes,as used for business cycles.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 4 / 49
Who Made It Happen
Solow 1956 extended Ramsey model of growth.by introducing technological change.simultaneously done by Swan 1956 in Australia.
Subsequent articles by Solow on "growth accounting"compute contribution of labor, capital, technological change.1957 "Technical Change & Aggregate Production Function"1960 "Investment and Technical Progress".
Ramsey�s 1928 set out dynamic optimization modelSolow worked on �rm side with constant savings rate.R.G.D.Allen�s 1968 Macro-Economic Theory :focus on growth but with no utility maximization.
1965 David Cass, T.C Koopmans independentlycombined Solow growth with Ramsey optimization:Ramsey-Cass-Koopmans neoclassical growth model.Brock and Mirman 1972 included uncertaintywith random shock in productivity, as in RBC.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 5 / 49
Causes of Sustained Growth
Shift up in output productivity parameter causes sustained growth.
Principle of sustained growth:
each factor of production must grow continuously.Physical capital factor, kt , can already grow:
kt+1 = kt (1� δk ) + it .
If it � δkkt , then capital is growing.
Need labor to grow as well, or "labor augmentation".
Productivity shift acts as labor augmentation.
Raw labor time cannot grow inde�nitely:
limited amount of time endowment.Growth models in essence must augment labor time
Total Factor Productivity (TFP) growth: common approach.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 6 / 49
Exogenous Technological Progress
TFP increase same as AG increaseLet AG depend on time: denoted AGt , where
yt = AGt (lt )γ (kt )
1�γ . (1)
Assume AGt grows at rate µ :
AGt+1 = AGt (1+ µ) , (2)
Re-write production function with AGt factoring labor time:
yt =hlt (AGt )
1γ
iγ(kt )
1�γ . (3)
De�ne AGt � (AGt )1γ , then
yt =�lt AGt
�γ(kt )
1�γ .
Result: if both factors lt AGt and kt grow at same ratethen output yt grows at that same rate.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 7 / 49
Stylized Growth Facts
Real wage rises over time
Real interest rate remains constant.
Output to capital ratio remains constant
Per capita income rises.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 8 / 49
Growth Facts by Assuming Trend in TFP
ytkt
=
�lt AGtkt
�γ
,
rt = MPkt = (1� γ)ytkt= (1� γ)
�lt AGtkt
�γ
=) ∆�lt AGtkt
�= 0; ∆ (lt ) = 0,=) ∆
�AGt
�= ∆kt
1+ g =yt+1yt
=
hlt+1 (AGt+1)
1γ
iγ(kt+1)
1�γhlt (AGt )
1γ
iγ(kt )
1�γ= (1+ µ)
�kt+1kt
�1�γ
,
kt+1kt
=
�1+ g1+ µ
� 11�γ
;
�AGt+1AGt
� 1γ
= (1+ µ)1γ .
=)�1+ g1+ µ
� 11�γ
= (1+ µ)1γ ; 1+ g = (1+ µ)
1γ
=) g =yt+1yt
=kt+1kt
' µ
γ.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 9 / 49
Growth Accounting
Baseline calibration: γ = 13 .
also assume growth rate of g = 0.03,
=) g = 0.03 = 3µ =µ
γ,
=) µ = 0.01.
g = µ+ (1� γ)kt+1kt
= µ+ (1� γ)µ
γ.
capital accounts for (1� γ)µγ = 2µ = 0.02,
two-thirds of total g = 0.03.Technology change: one-third of growth
Can be reinterpreted with endogenous growth, human capital.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 10 / 49
Balanced Growth Path Equilibrium
All variables that grow do so at common rate g .yt , ct , kt and it grow at rate g , for any t :
yt+1yt
=ct+1ct
=kt+1kt
=it+1it= 1+ g .
Time allocations xt , lt stationary along BGP : i.e. constant.Consumer Demand along BGP : kt+1kt = 1+ g ,
cdt = Twt lt + rtkt � kt+1 + kt (1� δk ) ,
= Twt lt + rtkt � kt (1+ g) + kt (1� δk ) ,
= Twt lt + kt (rt � δk � g) .
lt = 1� αctwt,
cdt =Twt + kt (rt � δk � g)
1+ α.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 11 / 49
Intertemporal Marginal Rate of Substitution along BGP
1+ g =(ct+1)
d
(ct )d =
1+ rt � δk1+ ρ
,
rt � δk = (1+ g) (1+ ρ)� 1,rt � δk � g = (1+ g) (1+ ρ)� 1� g = ρ (1+ g) .
cdt =1
1+ α[Twt + ktρ (1+ g)] ,
ypt � Twt + ktρ (1+ g) ,
cdt =ypt1+ α
.
Same as cdt =11+α (Twt + ktρ) when g = 0 in Part 4.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 12 / 49
AS-AD with Growth
ydt = cdt + st ; st = kst+1 � kst (1� δk ) , k
dt = k
st = kt ;
st = kst
�kst+1kst
� (1� δk )
�= kst [(1+ g)� (1� δk )] = k
st (g + δk ) .
ydt =Twt + ktρ (1+ g)
1+ α+ kt (g + δk ) ,
AD :1wt=
Tydt (1+ α)� kt [ρ (1+ g) + (g + δk ) (1+ α)]
y st = AG
�γAGwt
� γ1�γ
(kt )γ (kt )
1�γ = A11�γ
G
�γ
wt
� γ1�γ
kt ,
AS :1wt=
(y st )1�γ
γ
γA1γ
G (kt )1�γ
γ
.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 13 / 49
AS-AD Analysis: Example 11.1
γ = 13 , α = 0.5, ρ = 0.03, T = 1, δk = 0.03, AGt = 0.15;
g = 0.02; .kt = 1.0161.
1.02 = 1+ g = (1+ µ)1γ = (1+ µ)3 ,
µ = (1.02)13 � 1 = 0.0066227.
1wt
=T
ydt (1+ α)� kt [ρ (1+ g) + (g + δk ) (1+ α)]1wt
=1
ydt (1.5)� kt [0.03 (1.02) + (0.02+ 0.03) (1.5)], (4)
1wt
=(y st )
1�γγ
γA1γ
Gt (kt )1�γ
γ
1wt
=3 (y st )
2
(0.15)3 (1.0161)2. (5)
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 14 / 49
Shift Back in AS-AD with 2% Growth
0.0 0.1 0.2 0.3 0.40
5
10
15
20
Aggregate Output y
1/w
Figure 11.1. AS � AD Equilibrium With 2% Exogenous Growth and ZeroGrowth in Example 11.1.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 15 / 49
Recalibration: Example 11.2
With rt = (1+ g) (1+ ρ) + δk � 1,then g > 0 implies rt decreases; kt decreases.With r = 0.06 and g = 0.02, then change ρ :
rt = (1+ g) (1+ ρ) + δk � 1,rt = (1+ 0.02) (1+ ρ) + 0.03� 1 = 0.06;
ρ =1.03(1.02)
� 1 = 0.0098; =) kt = 2.7778.
1wt
=1
ydt (1.5)� 2.7778 [0.0098039 (1.02) + (0.02+ 0.03) (1.5)],
1wt
=3 (y st )
2
(0.15)3 (2.7778)2.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 16 / 49
AS-AD Shift Out, Wage the Same
0.0 0.1 0.2 0.3 0.40
5
10
15
20
Aggregate Output y
1/w
Figure 11.2. AS � AD Equilibrium With 2% Exogenous Growth and aLower Rate of Time Discount
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 17 / 49
Consumption and Output
cdt =1
1+ α[Twt + ktρ (1+ g)]
=23(0.13889+ (2.7778) (0.0098) (1.02)) = 0.1111.
ydt =1
1+ α(Twt + kt [ρ (1+ g) + (g + δk ) (1+ α)])
=23(0.1389+ (2.7778) ((0.0098) (1.02) + (0.05) (1.5))) = 0.25.
(δk + g) kt = (0.03+ 0.02) (2.7778) = 0.13889.
c falls by 20%, k, y rise by 20%, i rises by 100%.Consumption to output ratio falls from two-thirds to
cd
yd=0.11110.25
= 0.444.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 18 / 49
Labor Market
T � l st = xt =αctwt; cdt =
11+ α
[Twt + ktρ (1+ g)] ,
l st = T � α
1+ α
�T +
ktρ (1+ g)wt
�;
ldt =
�γAGwt
� 11�γ
kt .
wt =αktρ (1+ g)T � (1+ α) l st
=(0.5) (2.7778) (0.0098) (1.02)
1� (1.5) l st,
wt = γAG
�ktlt
�1�γ
=13(0.15)
�(2.7778)ldt
� 23
.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 19 / 49
Shift out in Labor Supply and Demand
0.2 0.3 0.4 0.5 0.6 0.7 0.8
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
Labor
w
Figure 11.3. Higher Employment, Same Wage, g = 0.02 of Example 11.2
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 20 / 49
The Exogenous Growth Process Over TimeExample 11.3. Continuous Shifts in Productivity
g = 0.02, µ = 0.00662.
AGt = 0.15, AGt+1 = 0.15 (1+ µ) .
AGt+1 = (0.15) (1.0066227) = 0.151,
AGt+2 = (0.150 99) (1.0066227) = 0.152,
AGt+3 = (0.15199) (1.0066227) = 0.153.
=) kt = 2.7778, kt+1 = 2.8331,
kt+2 = 2.89, kt+3 = 2.9478.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 21 / 49
AS-AD Over Time
1wt+1
=1
ydt+1 (1.5)� 2.8331 [(0.0098039) (1.02) + (0.05) (1.5)],
1wt+1
=3�y st+1
�2(0.15099)3 (2.8331)2
;
1wt+2
=1
ydt+2 (1.5)� 2.8898 [(0.0098039) (1.02) + (0.05) (1.5)],
1wt+2
=3�y st+2
�2(0.15199)3 (2.89)2
;
1wt+3
=1
ydt+3 (1.5)� 2.9478 [(0.0098039) (1.02) + (0.05) (1.5)],
1wt+3
=3�y st+3
�2(0.153)3 (2.9478)2
.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 22 / 49
Output and Real Wage Rises
0.23 0.24 0.25 0.26 0.27 0.285
6
7
8
9
10
Aggregate Output y
1/w
Figure 11.4. AS � AD Equilibria Over Time With 2% Exogenous Growthin Example 11.3.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 23 / 49
Labor Market
wt+1 =(0.5) (2.8331) (0.0098039) (1.02)
1� (1.5) l st+1,
wt+1 =13(0.15099)
�(2.8331) /
�ldt+1
�� 23;
wt+2 =(0.5) (2.8898) (0.0098039) (1.02)
1� (1.5) l st+2,
wt+2 =13(0.15199)
�(2.89) /
�ldt+2
�� 23;
wt+3 =(0.5) (2.9478) (0.0098039) (1.02)
1� (1.5) l st+3,
wt+3 =13(0.153)
�(2.9478) /
�ldt+3
�� 23.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 24 / 49
Labor Supply, Demand Shift Up, Employment Unchanged
0.590 0.595 0.600 0.605 0.610
0.135
0.140
0.145
0.150
0.155
0.160
Labor
Wage Rate w
Figure 11.5. Labor Market with 2% Exogenous Growth in Example 11.3.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 25 / 49
Consumption and Output
Consumption and Output grow at 2% rate:
cdt+1 =23(0.14166+ (2.8331) (0.0098) (1.02)) = 0.11333;
cdt+2 =23(0.144 49+ (2.89) (0.0098) (1.02)) = 0.11559;
cdt+3 =23(0.14739+ (2.9478) (0.0098) (1.02)) = 0.11791.
ydt+1 =23(0.142+ (2.83) ((0.0098) (1.02) + (0.05) (1.5))) = 0.255,
ydt+2 =23(0.144+ (2.89) ((0.0098) (1.02) + (0.05) (1.5))) = 0.260,
ydt+3 =23(0.147+ (2.95) ((0.0098) (1.02) + (0.05) (1.5))) = 0.265.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 26 / 49
Growth in Input Market SpaceIsocost Lines Over Time
ISOCOST : yt = wt lt + rtkt ,
0.25 = (0.13889) lt + (0.06) kt ,
kt =0.250.06
� (0.13889) lt0.06
;
kt+1 =0.254980.06
� (0.14166)0.06
lt+1;
kt+2 =0.260080.06
� (0.14449)0.06
lt+2;
kt+3 =0.26530.06
� (0.14739)0.06
lt+3
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 27 / 49
Growth in Input Market SpaceIsoquant Curves Over Time
ISOQUANT : 0.25 = yt = AG�ldt�γ(kt )
1�γ = 0.15�ldt� 13 γ(kt )
23 ,
kt+1 =
�(0.25498)0.15099
� 32
�ldt+1
� 12
;
kt+2 =
�(0.26008)0.15199
� 32
�ldt+2
� 12
;
kt+2 =
�(0.2653)0.153
� 32
�ldt+2
� 12.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 28 / 49
Growth in Input Market SpaceInput Ratios Over Time
ktlt
=2.77780.60
= 4.6297;
kt+1lt+1
=2.83310.60
= 4.7218;
kt+2lt+2
=2.890.60
= 4.816;
kt+3lt+3
=2.94780.60
= 4.913.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 29 / 49
Isocosts, Isoquants Shift up, Labor Unchanged
0.4 0.5 0.6 0.7 0.8 0.9
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
Labor
k Capital
Figure 11.6. Factor Market Equilibrium with 2% Exogenous Growth inExample 11.3.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 30 / 49
Growth in Output SpaceProduction Possibility Curves Over Time
cdt = y st � it = AG�ldt�γ(kt )
1�γ � (g + δk ) kt ,
cdt = (0.15)�ldt� 13(2.7778)
23 � (0.02+ 0.03) (2.7778) ;
cdt+1 = (0.15099)�ldt� 13(2.8331)
23 � (0.02+ 0.03) (2.8331) ;
cdt+2 = (0.15199)�ldt� 13(2.89)
23 � (0.02+ 0.03) (2.89) ;
cdt+3 = (0.153)�ldt� 13(2.9478)
23 � (0.02+ 0.03) (2.9478) ;
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 31 / 49
Growth in Output SpaceUtility Level Curves Over Time
u = ln ct + α ln xt = ln ct + α ln (1� lt ) ,�2.452 7 = ln 0.1111+ 0.5 ln 0.4,
�2.452 7 = ln ct + 0.5 ln (1� lt ) ,
ct =e ln 0.1111+0.5 ln 0.4
(1� lt )0.5; (6)
ct+1 =e ln 0.11333+0.5 ln 0.4
(1� lt+1)0.5; (7)
ct+2 =e ln 0.11559+0.5 ln 0.4
(1� lt+2)0.5; (8)
ct+3 =e ln 0.11791+0.5 ln 0.4
(1� lt+3)0.5. (9)
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 32 / 49
Growth in Output SpaceBudget Lines Over Time
cdt = wt l st + ρ (1+ g) kst ,
cdt = (0.13889) l st + (0.0098039) (1+ 0.02) (2.7778) ;
cdt+1 = (0.14166) l st+1 + (0.0098039) (1+ 0.02) (2.8331) ;
cdt+2 = (0.144 49) l st+2 + (0.0098039) (1+ 0.02) (2.8898) ;
cdt+3 = (0.14739) l st+3 + (0.0098039) (1+ 0.02) (2.9478) .
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 33 / 49
Production, Utility Shift up, Labor Unchanged
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.06
0.08
0.10
0.12
0.14
0.16
0.18
Labor
c
Figure 11.7. General Equilibrium Consumption and Utility Levels withExogenous Growth
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 34 / 49
Trend in Time Endowment
Aguiar, Hurst 2009: US 1965-2005
labor hours down 12%, leisure up 5%T = x + l , net decrease of 7% over 40 yearsT down by 0.00182 or 0.182% per yearover 40 years, since (1� 0.00182)40 = 0.937% decrease from 1.
New Experiment: Let T trend down, AG trend up
changing in opposite directions simultaneously,related to business cycle explanation:Chapters 3, 9 : T and AG increased in expansion.Now T trends down slightly by 0.182%while AG trends up more signi�cantly.by 0.72%.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 35 / 49
Example 11.4: Opposite Trends in Time, Productivity
AGt = 0.15, Tt = 1;
AGt+1 = 0.15108, Tt+1 = 1� 0.00182 = 0.99818;AGt+2 = 0.15216, Tt+2 = (0.99818) (1� 0.00182) = 0.9964;AGt+3 = 0.15327, Tt+3 = (0.99636) (1� 0.00182) = 0.9946.
kt = 2.7778, kt+1 = 2.8280, kt+2 = 2.8793., kt+3 = 2.9317,
g = 0.02.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 36 / 49
Example 11.4: AS-AD
1wt+1
=(0.99818)
ydt+1 (1.5)� (2.8331) [(0.0098) (1.02) + (0.05) (1.5)],
1wt+1
=3�y st+1
�2(0.15108)3 (2.8331)2
;
1wt+2
=(0.99636)
ydt+2 (1.5)� (2.89) [(0.0098) (1.02) + (0.05) (1.5)],
1wt+2
=3�y st+2
�2(0.15216)3 (2.89)2
;
1wt+3
=(0.99455)
ydt+3 (1.5)� (2.948) [(0.0098) (1.02) + (0.05) (1.5)],
1wt+3
=3�y st+3
�2(0.15327)3 (2.948)2
.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 37 / 49
AS-AD Shift Out, Wage Rises Over Time
0.23 0.24 0.25 0.26 0.27 0.285
6
7
8
9
10
Aggregate Output y
1/w
Figure 11.8. AS � AD Equilibria With AG Trending Up and T TrendingDown in Example 11.4.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 38 / 49
Labor Market Supply, Demand Over Time
wt+1 =(0.5) (2.8337) (0.0098039) (1.02)
(0.99818)� (1.5) l st+1,
wt+1 =13(0.15108)
h(2.8331) /
�ldt+1
�i 23;
wt+2 =(0.5) (2.89) (0.0098039) (1.02)
(0.99636)� (1.5) l st+2,
wt+2 =13(0.15216)
h(2.8902) /
�ldt+2
�i 23;
wt+3 =(0.5) (2.948) (0.0098039) (1.02)
(0.99455)� (1.5) l st+3,
wt+3 =13(0.15327)
h(2.948) /
�ldt+3
�i 23.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 39 / 49
Labor Supply Shifts Back with Hours Falling
0.590 0.595 0.600 0.605 0.610
0.135
0.140
0.145
0.150
0.155
0.160
Labor
Wage Rate w
Figure 11.9. Labor Market with AG Trending Up and T Trending Down inExample 11.4.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 40 / 49
Employment Falls Slightly Over Time
lt = 0.6,
lt+1 = (0.6) (1� 0.00182) = 0.598 91,lt+2 = (0.598 91) (1� 0.00182) = 0.597 82,lt+3 = (0.597 82) (1� 0.00182) = 0.596 73.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 41 / 49
TFP, Japan�s Lost Decade, Minnesota School
AGt :"total factor productivity", or TFP, the "Solow residual".Much research computing TFP, including over time
Hayashi and Prescott 2002: Japan�s 1990s stagnation
"lost decade" explained by a low TFP.TFP accounting used both for growth, business cyclesgiven the cycle is more of a longer term,like occasional change in the trend growth rate.
Kehoe, Prescott 2002 "Great Depressions of the Twentieth Century",
known as "Minnesota approach", including1930s depression in Germany, France, Italy, US and UK,1980s contractions in Argentina, Mexico, Chile1990s Japan .
Extended in Chari et al 2007 "Business Cycle Accounting".
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 42 / 49
Appendix A.11: Solution Methodology for ExogenousGrowth
1+ g =ct+1ct
=1+ rt � δk1+ ρ
,
=) g (1+ ρ) + ρ+ δk = rt = (1� γ)AG
�ltkt
�γ
,
=) ltkt=
�g (1+ ρ) + ρ+ δk
(1� γ)AG
� 1γ
;wt = γAG
�ltkt
�γ�1
ydt =wtT + kt [ρ (1+ g) + (1+ α) (g + δk )]
1+ α= AG
�ltkt
�γ
kt = y st .
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 43 / 49
Solving for the Capital Stock from AS-AD
Substitute into ydt = yst equation for w as a function of
ltkt
from marginal product of labor,
and substitute in for ltkt,
solved from intertemporal marginand the marginal product of capital.
=) kt =
Tγ (AG )1γ
�(1�γ)
g (1+ρ)+ρ+δk
� 1�γγ
(1+ α) δk
�γ
(1�γ)
�+ (1+ α)
�g (1+ρ)+ρ(1�γ)
�� [ρ (1+ g) + (1+ α) g ]
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 44 / 49
Example 11.1: Capital Stock Solution
γ = 13 , α = 0.5, ρ = 0.03, T = 1, δk = 0.03, AGt = 0.15, g = 0.02.
=) kt = 1.0161 =
(0.15)3�
23(0.02(1.03)+0.03+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.03)+0.03)
2
�� (0.03 (1.02) + (1.5) (0.02))
�g = 0.04 instead of g = 0.02, then the capital stock falls almost by half to0.53357 :
g = 0.04 =) kt = 0.53357 =
(0.15)3�
23(0.04(1.03)+0.03+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.04(1.03)+0.03)
2
�� (0.03 (1.04) + (1.5) (0.04))
� ,Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 45 / 49
Examples 11.2: Capital Stock Solution
r = 0.06, g = 0.02, ρ = 0.0098039
=) kt = 2.7778 =
(0.15)3�
23(0.02(1.0098)+0.0098+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.0098)+0.0098)
2
�� (0.0098 (1.02) + 0.03)
�
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 46 / 49
Examples 11.3: Continuous Productivity Increase
=) kt+1 = 2.8331 =
(0.15099)3�
23(0.02(1.0098039)+0.0098+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.0098)+0.0098)
2
�� (0.0098 (1.02) + 0.03)
� .=) kt+2 = 2.89 =
(0.15199)3�
23(0.02(1.0098)+0.0098+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.0098)+0.0098)
2
�� (0.0098 (1.02) + 0.03)
�=) kt+3 = 2.9478 =
(0.153)3�
23(0.02(1.0098)+0.0098+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.0098)+0.0098)
2
�� (0.0098 (1.02) + 0.03)
� .Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 47 / 49
Examples 11.4: Trends in Time, Goods
=) kt+1 = 2.8337 =
0.99818 (0.15108)3�
23(0.02(1.0098)+0.0098+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.0098)+0.0098)
2
�� (0.0098 (1.02) + 0.03)
�=) kt+2 = 2.8902 =
0.99636 (0.15216)3�
23(0.02(1.0098)+0.0098+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.0098)+0.0098)
2
�� (0.0098 (1.02) + 0.03)
�=) kt+3 = 2.9480 =
0.99455 (0.15327)3�
23(0.02(1.0098)+0.0098+0.03)
�23�(1.5) (0.03) (0.5) + 1.5
�3(0.02(1.0098)+0.0098)
2
�� (0.0098 (1.02) + 0.03)
�Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 48 / 49
Examples 11.4: Growth Rate
kt+1kt
=
Tt+1γ(AGt+1)1γ�
(1�γ)g (1+ρ)+ρ+δk
� 1�γγ
(1+α)δk�
γ(1�γ)
�+(1+α)
�g (1+ρ)+ρ(1�γ)
��[ρ(1+g )+(1+α)g ]
Ttγ(AGt )1γ�
(1�γ)g (1+ρ)+ρ+δk
� 1�γγ
(1+α)δk�
γ(1�γ)
�+(1+α)
�g (1+ρ)+ρ(1�γ)
��[ρ(1+g )+(1+α)g ]
,
kt+1kt
=Tt+1 (AGt+1)
1γ
Tt (AGt )1γ
=Tt (1� 0.00182) [AGt (1.0072)]
1γ
Tt (AGt )1γ
= (1� 0.00182) (1.0072)3 = 1.02.
Gillman (University of Missouri-St. Louis) Chapter 11 10 October 2016 49 / 49