### Leontief Economic Models Section 10.8 Presented by Adam Diehl

```Leontief Economic Models
Section 10.8
From Elementary Linear Algebra: Applications Version
Tenth Edition
Howard Anton and Chris Rorres
Wassilly Leontief
Nobel Prize in Economics 1973.
Taught economics at Harvard and New York
University.
Economic Systems
• Closed or Input/Output Model
– Closed system of industries
– Output of each industry is consumed by industries
in the model
• Open or Production Model
– Incorporates outside demand
– Some of the output of each industry is used by
other industries in the model and some is left over
to satisfy outside demand
Input-Output Model
• Example 1 (Anton page 582)
Work Performed by
Carpenter
Electrician
Plumber
Days of Work in Home of Carpenter
2
1
6
Days of Work in Home of
Electrician
4
5
1
Days of Work in Home of Plumber
4
4
3
Example 1 Continued
p1 = daily wages of carpenter
p2 = daily wages of electrician
p3 = daily wages of plumber
Each homeowner should receive that same
value in labor that they provide.
Solution
1
31
2 =  32
3
36
Matrices
Exchange matrix
Price vector
.2 .1
= .4 .5
.4 .4
1
= 2
3
Find p such that
=
.6
.1
.3
Conditions

0 for  = 1,2, … , k

0 for ,  = 1,2, … , k

=1
= 1 for  = 1,2, … , k
Nonnegative entries and column sums of 1 for E.
Key Results
=
− =
This equation has nontrivial solutions if
det  −  = 0
Shown to always be true in Exercise 7.
THEOREM 10.8.1
If E is an exchange matrix, then  =  always
has a nontrivial solution p whose entries are
nonnegative.
THEOREM 10.8.2
Let E be an exchange matrix such that for some
positive integer m all the entries of Em are
positive. Then there is exactly one linearly
independent solution to  −   = , and it
may be chosen so that all its entries are positive.
For proof see Theorem 10.5.4 for Markov chains.
Production Model
• The output of each industry is not completely
consumed by the industries in the model
• Some excess remains to meet outside demand
Matrices
Production vector
Demand vector
Consumption matrix
1
2
= ⋮

1

= 2
⋮

11
21
= ⋮
1
12
22
⋮
2
⋯ 1
⋯ 2
⋱
⋮
⋯
Conditions

0 for  = 1,2, … , k

0 for  = 1,2, … , k

0 for ,  = 1,2, … , k
Nonnegative entries in all matrices.
Consumption
11 1 + 12 2 + ⋯ + 1
21 1 + 22 2 + ⋯ + 2
=
⋮
1 1 + 2 2 + ⋯ +
Row i (i=1,2,…,k) is the amount of industry i’s
output consumed in the production process.
Surplus
Excess production available to satisfy demand is
given by
−  =
(I − ) =
C and d are given and we must find x to satisfy
the equation.
Example 5 (Anton page 586)
• Three Industries
– Coal-mining
– Power-generating
x1 = \$ output coal-mining
x2 = \$ output power-generating
Example 5 Continued
0 .65
= .25 .05
.25 .05
50000
= 25000
0
.55
.10
0
Solution
102,087
= 56,163
28,330
Productive Consumption Matrix
If ( − ) is invertible,
= (I − )−1
If all entries of (I − )−1 are nonnegative there
is a unique nonnegative solution x.
Definition: A consumption matrix C is said to be
productive if (I − )−1 exists and all entries of
(I − )−1 are nonnegative.
THEOREM 10.8.3
A consumption matrix C is productive if and only
if there is some production vector x 0 such
that x Cx.
For proof see Exercise 9.
COROLLARY 10.8.4
A consumption matrix is productive if each of its
row sums is less than 1.
COROLLARY 10.8.5
A consumption matrix is productive if each of its
column sums is less than 1.
(Profitable consumption matrix)
For proof see Exercise 8.
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