This paper extends the standard neoclassical model by considering a technology sector through which an economy with limited human capital attempts to catch up with a given "locomotive" pushing exogenously technical progress. In periods of technological stagnation, economies close enough to the frontier may find it optimal to not catch up, which reinforces worldwide technological sclerosis. Under sustainable technological growth, all the other economies will sooner or later engage in imitation. Such a phase of technology adoption may be delayed depending on certain deep characteristics of the followers.

Benteng Zou

Raouf Boucekkine

English

Research Papers in Economics

Institute of
Mathematical
Economics
Working Papers
428
March 2010
Catching-up with the ”locomotive”: a simple
theory
Raouf Boucekkine and Benteng Zou
IMW · Bielefeld University
Postfach 100131
33501 Bielefeld · Germany
email: imw@wiwi.uni-bielefeld.de
http://www.wiwi.uni-bielefeld.de/˜imw/Papers/showpaper.php?428
ISSN: 0931-6558Catching-up with the “locomotive”: a simple theory¤
Raouf Boucekkine y Benteng Zouz
March 4, 2010
Abstract
This paper extends the standard neoclassical model by considering a technology sector
through which an economy with limited human capital attempts to catch up with a given
“locomotive” pushing exogenously technical progress. In periods of technological stagna-
tion, economies close enough to the frontier may ﬁnd it optimal to not catch up, which
reinforces worldwide technological sclerosis. Under sustainable technological growth, all
the other economies will sooner or later engage in imitation. Such a phase of technology
adoption may be delayed depending on certain deep characteristics of the followers.
1 Introduction
The neoclassical theory of economic growth (Solow, 1957) entails the idea of an economic loco-
motive driving worldwide technological progress through the assumption of exogenous tech-
nological progress. Related concepts like convergence and catching-up have been developed
along the way (see one of the numerous textbooks in economic growth, like Barro and Sala-
i-Martin, 1995). However, in this benchmark, convergence refers to the level of income per
capita being equalized in the long-run under certain assumptions, and in particular assuming
that all countries have immediate access to the same technology at no cost. It is now widely
¤
yCORE and IRES, Catholic University of Louvain, and department of economics, University of Glasgow, Place
Montesquieu 3, Louvain-La-Neuve, Belgium. Tel: (32)10 47 3848. E-mail: raouf.boucekkine@uclouvain.be.
zCREA, University of Luxembourg, 162A, avenue de la Faiencerie, L-1151, Luxembourg. E-
mail:benteng.zou@uni.lu.admitted that such an assumption is heroic, under-development principally originates in the
difﬁculty of transferring top technologies to countries with very limited technological absorp-
tion capacity due to the scarcity of human capital. This note revisits the neoclassical growth
model by introducing a technology adoption variable into the benchmark and bringing the
limited human capital resources into the analysis. To unburden the analysis, we shall assume
that human capital resources are ﬁxed for ever. These resources should be allocated between
technology adoption (or imitation of a given economic growth locomotive in the neighborhood
of the economy) and production of the ﬁnal good. Technological evolution follows a catching-
up equation pretty much in line with Nelson and Phelps (1966), as recently resumed by Ben-
habib and Spiegel (1994) and Boucekkine et al. (2006). The paper derives optimal adoption
policies and their implications for the long-term technological gap between the locomotive and
the follower depending on the strength of the locomotive’s economic growth. We show how
the latter aspect dramatically shape the outcomes of the model (nonzero or zero long-run tech-
nological gap, adoption delays, etc...). In periods with no signiﬁcant technological progress
(i.e, pre-industrial periods), economies close enough to the technological frontier may ﬁnd it
optimal to not catch up with the locomotive, which reinforces worldwide technological sclero-
sis. When the locomotive economy experiences sustainable technological growth, then all the
other economies will sooner or later engage in imitation. Such a phase of technology adoption
may be delayed depending on certain deep characteristics of the followers. Our model delivers
therefore a simple non-strategic theory of adoption delays.
2 The model
Suppose that the economy is populated by inﬁnitely lived agents with a strictly increasing and
concave consumption-based utility function U(C(t)). For simplicity, we normalize population
size to 1. We also model normalize total human capital available in this economy to 1 to reﬂect
scarcity as outlined above. A benevolent planner aims at maximizing the welfare of the econ-
omy by choosing the optimal human capital allocation across the ﬁnal good and the technology
sectors, and the optimal consumption plan over time:
max
u(t);l(t);C(t)
Z 1
0
e¡½tU(C(t))dt; (1)
2with ½ time preference, subject to:
Y (t) = A(t)K(t)®l(t)1¡®; (2)
_ A = Á(t)u(t)
¡
A0(t) ¡ A(t)
¢
; (3)
_ K = I(t) ¡ ±K(t) = Y (t) ¡ C(t) ¡ ±K(t); (4)
and the resource constraint
u(t) + l(t) = 1;0 · u(t);0 · l(t): (5)
Equation (2) gives the production function which is the usual neoclassical one: K(t) is the
stock of capital at t, l(t) is production human capital, and ® is capital share. A(t) is the level of
technology, and in contrast to the standard neoclassical model, we assume that it follows the
dynamic law of motion (3), which features a kind of output of a technology sector. The econ-
omy imitates the technology of the regional locomotive, here A0(t), u(t) is human capital in the
technology sector, and Á(t)(< 1) is an exogenous variable indexing the learning (or absorbing
capacity) of this economy. Just like in standard endogenous growth theory (see Romer, 1990),
weassumeconstantreturntohumancapitalinthetechnologysector. WealsoassumethatA0(t)
grows at constant exogenous rate ° ¸ 0: A0(t) = A0e°t, 8t ¸ 0. Initially, K(0) and A(0) < A0(0)
are given: the technology of our economy is lagged with respect to the locomotive.
The optimal control problem above (with control) constraints is standard, and can be handled
using the Lagrangean:
L = U(C(t)) + ¹1(t)
¡
A(t)K®l1¡® ¡ C ¡ ±K
¢
+ ¹2(t)Á(t) u
¡
A0(t) ¡ A(t)
¢
+»(t)u(t) + ´(t)l(t) + w(t)(1 ¡ u(t) ¡ l(t));
where ¹1(t) and ¹2(t) are the costate variables associated with capital and technology stocks
respectively, w(t) is the Lagrange multiplier associated with human capital resource constraint
(thereforerepresentingtheshadowwageorshadowremunerationofhumancapital), and» and
´(t) are the Kuhn-Tucker multipliers for nonnegative constraints on the allocation of human
capital across the two sectors. The ﬁrst-order necessary (and sufﬁcient) conditions are:
¹1(t) = U0(C); (6)
3_ ¹1(t) = ½¹1 ¡ ¹1(®AK®¡1l1¡® ¡ ±); (7)
_ ¹2(t) = ½¹2 ¡
£
¹1K®l1¡® ¡ ¹2(t)Á(t)u
¤
; (8)
@L
@u
= ¹2(t)Á(t)
¡
A0(t) ¡ A(t)
¢
+ »(t) ¡ w(t) · 0; »t ¸ 0; »tut = 0; (9)
with equality if ut > 0,
@L
@l
= ¹1(t)(1 ¡ ®)A(t)K®l¡® + ´(t) ¡ w(t) · 0; ´t ¸ 0; ´tlt = 0; (10)
withequalityiflt > 0, andthetransversalityconditions lim
t!1
e¡½t¹1K(t) = 0;and lim
t!1
e¡½t¹2A(t) =
0. The conditions are standard. In particular, (9) and (10) are the optimality conditions with
respect human capital shares in the technology and ﬁnal good sectors respectively. The both
account for scarcity of human capital and for the non-negativity constraints (in the standard
way). Notice that by (10) the corner solution l(t) = 0 is impossible (since ® < 1). However,
both the corner and interior solutions are possible for u(t) resulting in different technological
development paths, as explained below. From now on, we assume a logarithmic utility func-
tion and Á(t) = Á > 0 for simplicity.
3 Main results
Deﬁne the balanced growth paths (BGP) as particular solutions to the optimality conditions
and feasibility constraints listed in Section 2 such that human capital allocation across sectors
is time-independent and variables K(t), C(t) and A(t) grow at non-negative rates. We denote
the growth rate of variable X as gX. We are able to gather the following two main results.
3.1 Catching-up in periods of technological stagnation
This pre-industrial case corresponds to ° = 0 in our model. This case is characterized by the
following proposition.
Proposition 1 Suppose ° = 0 and A0(t) = A0(0).
(i) u(t) = 0, for all t ¸ 0, is an optimal choice if
A0(0)
A(0)
· 1 +
½(1 ¡ ®)
Á
: (11)
4(ii) Otherwise, if
A0(0)
A(0) > 1+
½(1¡®)
Á , there exists t > 0, such that, catching up in technology happens
at t where A(t) = A0(0);8t ¸ t and u(t) =
8
<
:
> 0; 80 < t < t;
= 0; 8t ¸ t:
Condition (11) puts an upper bound on the initial technological gap: if it is low enough, that
is if the technological frontier is close enough, then the economy may not devote any effort to
technological catching-up: the productivity gain in doing so does not compensate for the loss
in consumption (and therefore in welfare) coming from diverting human capital from the ﬁnal
good sector to the technology sector. Notice that the upper bound in (11) is increasing in the
discount rate, ½, and decreasing in the learning parameter, Á: the lower the weight assigned
to the future and the less efﬁcient is learning in technology, the wider the range of initial sit-
uations that can potentially induce this case of technological sclerosis. In contrast, when the
economy is far enough the frontier, investing human capital in technological upgrading makes
sense, and the economy eventually catches up the stagnant locomotive at ﬁnite time. But since
leapfrogging is not optimal in our model, this case also yields technological sclerosis at ﬁnite
time. Interestingly enough, transitory periods of technological progress only occur in the most
lagged countries (relative to the locomotive) in such a stagnant environment featuring the pre-
industrial era.
3.2 Catching-up with a growing “locomotive”
We now consider the more contemporaneous case of locomotives growing at strictly positive
growth rates. The induced technological evolution in the follower countries is then drastically
different from the one featured for the stagnation case above.
Proposition 2 Let ° > 0.
(i) The necessary condition for u = 0 to be optimal is
A0(0)
A(0) · 1 +
½(1¡®)
Á : Furthermore, u = 0 can
only be optimal for a ﬁnite time adjustment period, that is when t · 1
° ln
³
[½(1¡®)+Á]A(0)
ÁA0(0)
´
:
(ii) Along the BGP, all the variables, except u, grow at constant rates gA = °; gC = gK = gY =
°
1¡®: The human capital share in the technology sector is the unique positive solution of
°(1¡u)
(1¡®)u =
½+° +Áuµ: It is increasing in the rate of technological progress carried out by the leader, du
d° > 0.
5The proposition has several interesting results. In contrast to periods of technological stagna-
tion, having a growing locomotive always prevents from getting into technological sclerosis in
the long-run. As in the standard neoclassical growth model, BGPs exist with the growth rate
of technology equal to the locomotive’s. Moreover, the faster the locomotive, the more human
capital the economy will put in the technology sector (although A(t) will not converge in level
to A0(t)). Nonetheless, the economy can choose to experience a period of zero technological
progress, exactly as in the stagnation case studied above and under the same condition on the
initial technological gap. However, this period is transitory, and it features a kind of adoption
delay. Adoption is delayed because the planner ﬁnds it optimal to put all the human capital
resources in the ﬁnal good sector in the short-run (given the weight assigned to present con-
sumption) and to take advantage of the technological push of the locomotive in later stages
(when the weight assigned to consumption is low enough). In this sense, this paper uncovers a
new case for delaying adoption (see Boucekkine et al., 2004, for more insight into the literature
of adoption delays). The lower the initial technological gap, the longer the adoption delay. The
delay is also decreasing in the exogenous pace of technological progress, °, and learning, Á,
while it grows with the discount rate, ½.
References
[1] Benhabib, J. and D. Spiegel (1994), “The Role of human capital in economic development:
Evidence from aggregate cross-country data, Journal of Monetary Economics 34, 143-173.
[2] Boucekkine R., B. Martinez, and C. Saglam (2006), “The development problem under em-
bodiment”, Review of Development Economics 10, 42-58.
[3] Boucekkine, R., C. Saglam and T. Vall´ ee (2004), “Technology Adoption Under Embodi-
ment: A Two-Stage Optimal Control Approach”, Macroeconomic Dynamics 8, 250-271.
[4] Nelson R. and E. Phelps (1966), “Investment in humans, technology diffusion and eco-
nomic growth”, American Economic Review 56, 69-75.
[5] Romer, P. (1990),“Endogenous technicnological change”, Journal of Political Economy 98,
71-102.
6Appendix (not intended for publication)
A. Lemma
Before the main result, we have the following lemma which is used in the proof of the proposi-
tion.
Lemma 1 If there is a balanced growth path and 0 < u(t) < 1, then along the BGP, u(t) = u 2 (0;1)
is a constant.
ProofIfthereisBGP,thenalongtheBGP,themarketclearingcondition(5)isuegut+leglt = 1,
where constants u and l are labors in different sectors when the BGP starts.
Due to the fact that labor force is ﬁnite, the growth rates gu and gl can not be both positive
and from market clearing condition can not be both negative. As mentioned previously l = 0
cannot be optimal, hence we must have gl = 0. For the case u > 0, we must also have gu = 0.
Therefore gu = gl = 0 and along the BGP both u and l are positive constants with u + l = 1:
We ﬁnish the proof.
B. Proof Proposition 1: ° = 0 and A0(t) = A0(0)
Suppose the optimal balanced growth path starts from some time t = e t ¸ 0 and along the BGP
u(t) = 0 for t ¸ e t. Then from labor market clearing condition, we have l(t) = 1. Obviously, it is
possible that e t = 0, where there is no imitation at all; or e t > 0, which reads there may be some
imitation during some period until e t.
In the case of no imitation, e t = 0, the state equations and the ﬁrst order conditions are
8
> > > > > > > > > > > <
> > > > > > > > > > > :
_ K = A(t)K® ¡ C(t) ¡ ±K(t);
_ A = 0;
_ C
C = ®A(t)K®¡1 ¡ (½ + ±);
_ ¹2(t) = ½¹2 ¡
K®
C
;
¹2(t)Á
¡
A0(t) ¡ A(t)
¢
+ »(t) ·
(1 ¡ ®)A(t)K®
C
(= w(t));
» ¸ 0:
(12)
7The 2nd equations reads A(t) = A(0) < A0(t) for all t > 0. Hence the 3rd equations shows
that gC + (½ + ±) = ®A(0)K(t)®¡1 which holds if and only if K(t) = K is a constant. And
the 1st equations presents gC = 0. As by products, we also have K =
µ
½ + ±
®A(0)
¶ 1
®¡1
; C =
K®(A(0) ¡ ±K1¡®): Therefore, consumption-capital ratio is
C
K
=
½ + (1 ¡ ®)±
®
:
The 4th equations in (12) leads to
_ ¹2
¹2
= g¹2 = ½ ¡
K®
C¹2
which is a constant if and only if
¹2(t) = ¹2 is a constant (or g¹2 = 0). Moreover, ¹2 =
1
½
K
C
K®¡1 =
½ + ±
½(½ + ±(1 ¡ ®))A(0)
:
Combining the last two inequalities in (12), it yields
0 · » · (1 ¡ ®)A(0)K®¡1 K
C ¡ Á¹2(A0(0)e°t ¡ A(0))
=
½ + ±
½(½ + ±(1 ¡ ®))
[½(1 ¡ ®) + Á)]A(0) ¡ ÁA0(0)e°t
A(0)
:
(13)
With ° = 0, the necessary condition for the above inequality holds is [½(1 ¡ ®) + Á]A(0) ¡
ÁA0(0) ¸ 0 or equivalently
A0(0)
A(0)
·
½(1 ¡ ®) + Á
Á
= 1 +
½(1 ¡ ®)
Á
:
Whene t > 0 and u > 0 for at least 0 < t < e t, the state equations and the ﬁrst order conditions
are 8
> > > > > > > > > > <
> > > > > > > > > > :
¹2(t)Á
¡
A0(t) ¡ A(t)
¢
=
(1 ¡ ®)A(t)K®(1 ¡ u(t))¡®
C
(= w(t));
_ K = A(t)K®(1 ¡ u(t))1¡® ¡ C(t) ¡ ±K(t);
_ A = Áu(A0(t) ¡ A(t));
_ C
C
= ®A(t)K®¡1(1 ¡ u(t))1¡® ¡ (½ + ±);
_ ¹2(t) = (½ + Áu)¹2(t) ¡
K®(1 ¡ u(t))1¡®
C
:
(14)
Substituting the 3rd equation into the 1st one, it yields¹2
_ A
A
= ¹2gA =
(1 ¡ ®)uK®(1 ¡ u(t))¡®
C
:
Dividing the 3rd equation by A(t) leads to gA = Áu
µ
A0(0)
A
e(°¡gA)t ¡ 1
¶
, which is a constant if
and only if gA = ° where A is the technology level along BGP. The situation of ° is zero or not,
the results are different.
With ° = 0, it must follow, from the 3rd equation, A(t) = A0(t) = c A0 which is the catching-
up steady state.
8If the leading technology reaches its steady state while the underdeveloped one keeps im-
itation, sooner or later, the underdeveloped one will catch up to the steady state level of the
leader. Furthermore, since along the BGP, u is constant and there is nothing more to learn,
hence, we must have along the BGP, u = 0.
We denote this special time e t = t. Hence, we can conclude that before t, there is imitation
and u > 0. From t = t, there is catch-up in technology and no need for imitation, u = 0;8t > t.
That ﬁnishes the proof.
C. Proof Proposition 2: ° > 0
Part (i) Notice, u = 0 is one of the solutions and is sufﬁcient for the optimization problem due
to Kuhn-Tucker condition. Then, repeating the proof of Proposition 1 until (13), with ° > 0, the
necessary condition for the last inequality in (13) is
[½(1 ¡ ®) + Á]A(0)
ÁA0(0)
¸ e°t or t ·
1
°
ln
µ
[½(1 ¡ ®) + Á]A(0)
ÁA0(0)
¶
which makes sense if
[½(1 ¡ ®) + Á]A(0) ¸ ÁA0(0):
Therefore, thenecessaryconditionforu = 0tobeanoptimalsolutionis
A0(0)
A(0)
·
½(1 ¡ ®) + Á
Á
=
1 +
½(1 ¡ ®)
Á
and maximum time is t ·
1
°
ln
µ
[½(1 ¡ ®) + Á]A(0)
ÁA0(0)
¶
.
Part (ii) With u > 0 and slackness condition in (9), we must have » = 0. Hence, the state
equations and the ﬁrst order conditions are given by (14).
Suppose there is BGP, and by Lemma 1, it follows u(t) = u.
Substituting the 3rd equation of (14) into the 1st one, it yields
¹2
_ A
A
= ¹2gA =
(1 ¡ ®)uK®(1 ¡ u(t))¡®
C
(15)
where A is the technology level along BGP.
Dividing the 3rd equation by A(t), it yields gA = Áu
µ
A0(0)
A
e(°¡gA)t ¡ 1
¶
which is a con-
stant if and only if gA = °. With ° > 0, along the BGP, the 4th equation reads gC = ®Ae°t(1 ¡
9u)1¡®K
®¡1egK(®¡1)t ¡ (½ + ±); or
gK =
°
1 ¡ ®
gC + ½ + ± = ®(1 ¡ u)1¡®AK
®¡1: (16)
The 5th equation is equivalent to
_ ¹2
¹2
= ½+Áu¡
(1 ¡ u)1¡®K®
¹2C(t)
: Substituting (15) into it, we
have
g¹2 = ½ + Áu ¡
(1 ¡ u)°
(1 ¡ ®)u
: (17)
Dividing the 2nd equation by K(t) and rearranging the term, il yields gK = AK
®¡1(1 ¡
u)1¡®e(gA¡(1¡®)gK)t ¡ ± ¡
C
K
e(gC¡gK)t: Since gA = ° = (1 ¡ ®)gK, it must follow
gC = gK =
°
1 ¡ ®
; gK = AK
®¡1(1 ¡ u)1¡® ¡ ± ¡
C
K
: (18)
Combining(18)and(16), weobtain
°
1 ¡ ®
+½+± = ®(1¡u)1¡®AK
®¡1 = ®
µ
°
1 ¡ ®
+ ± +
C
K
¶
:
Hence, consumption-capital ratio along the BGP is
C
K
=
° + (1 ¡ ®)± + ½
®
: (19)
Taking derivative of (15), diving by ¹2, and rearranging terms, it follows
gmu2 = ®gK ¡ gC = ¡°: (20)
Combining (20) and (17), il yields
°(1 ¡ u)
(1 ¡ ®)u
= ½ + ° + Áu; u > 0: (21)
Deﬁne f(u) = ½ + ° + Áu, g(u) =
°(1 ¡ u)
(1 ¡ ®)u
. It is easy to check f(0) = ½ + ° > 0; f0(u) >
0; f(1) = ½ + ° and lim
u!0
g(u) = +1; g0(u) = ¡
°
(1 ¡ ®)u2 < 0; g(1) = 0. Therefore, (21) gives
one and only one solution of u, such that 0 < u < 1.
Effect of °. Let us now prove that u is increasing with respect with °.
Taking total differential with respect to ° and u in equation (21) and rearranging terms, il
follows
[°(2 ¡ °) + ½(1 ¡ ®) + 2(1 ¡ ®)u]du = (1 ¡ (2 ¡ ®)u)d°:
10Hence,
du
d°
=
1 ¡ (2 ¡ ®)u
B(°;u)
;
where B(°;u) = °(2¡°)+½(1¡®)+2(1¡®)u is always positive, as long as ° · 2. Therefore,
the sign of du
d° will only depend on (1 ¡ (2 ¡ ®)u).
Denote X(u) = 1 ¡ (2 ¡ ®)u. It is easy to check X(0) = 1, X(1) = ¡(1 ¡ ®) < 0 and
X0(u) = ¡(2 ¡ ®) < 0; that is, X(u) is decreasing in term of u 2 (0;1). And at u¤ = 1
2¡®,
X(u¤) = 0.
Furthermore, f(u¤) = ½ + ° + Á(u¤) and g(u¤) = ° < f(u¤), which states that u < u¤. And
hence at u, X(u) > 0. As a result, it yields du
d° > 0. We ﬁnish the proof.
11

Investment in humans, technology diffusion and economic growth”,

technicnological change”,

Technology Adoption Under Embodiment: A Two-Stage Optimal Control Approach”,

The development problem under embodiment”,

The Role of human capital in economic development: Evidence from aggregate cross-country data,

Catching-up with the "locomotive": a simple theory

http://www.imw.uni-bielefeld.de/papers/files/imw-wp-428.pdf

Catching-up with the "locomotive": a simple theory

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