ch. 12 optimization with equality constraints

54
1 Ch. 12 Optimization with Equality Constraints 12.1 Effects of a Constraint 12.2 Finding the Stationary Values 12.3 Second-Order Conditions 12.4 Quasi-concavity and Quasi- convexity 12.5 Utility Maximization and Consumer Demand 12.6 Homogeneous Functions 12.7 Least-Cost Combination of Inputs 12.8 Some concluding remarks

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Ch. 12 Optimization with Equality Constraints. 12.1Effects of a Constraint 12.2Finding the Stationary Values 12.3Second-Order Conditions 12.4Quasi-concavity and Quasi-convexity 12.5Utility Maximization and Consumer Demand 12.6Homogeneous Functions - PowerPoint PPT Presentation

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Page 1: Ch. 12 Optimization with Equality Constraints

1

Ch. 12 Optimization with Equality Constraints

• 12.1 Effects of a Constraint• 12.2 Finding the Stationary Values• 12.3 Second-Order Conditions• 12.4 Quasi-concavity and Quasi-

convexity• 12.5 Utility Maximization and

Consumer Demand• 12.6 Homogeneous Functions• 12.7 Least-Cost Combination of Inputs• 12.8 Some concluding remarks

Page 2: Ch. 12 Optimization with Equality Constraints

2

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Page 4: Ch. 12 Optimization with Equality Constraints

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Page 5: Ch. 12 Optimization with Equality Constraints

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Page 6: Ch. 12 Optimization with Equality Constraints

6

12.2-2 Total-differential approach

• dL = fxdx + fydy = 0 differential of L=f(x,y)

• dg = gxdx + gydy = 0 differential of g=g(x,y)

• dx & dy dependent on each other

• dy/dx = -fx/ fy slope of isoquant curve

• dy/dx = -gx/gy slope of the constraint line

• -gx /gy = -fx/ fy equal at the tangent

• fx/ gx = fy /gy = equi-marginal principle

Page 7: Ch. 12 Optimization with Equality Constraints

7

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Page 8: Ch. 12 Optimization with Equality Constraints

8

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Page 9: Ch. 12 Optimization with Equality Constraints

9

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Page 10: Ch. 12 Optimization with Equality Constraints

10

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Page 11: Ch. 12 Optimization with Equality Constraints

11

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Page 12: Ch. 12 Optimization with Equality Constraints

12

361 p. W,&C;

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Where

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max(:definite negative0)1,...(0,0,0H

361) (p. soc, case variablend)

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max(:definite negative0,0H

soc of test variable3c)

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max(:definite negative0H

soc of test variable2b)

constraint than variablemore one

bemust therebecause test variable-one No a)

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Page 13: Ch. 12 Optimization with Equality Constraints

13

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Page 14: Ch. 12 Optimization with Equality Constraints

14

12.2 Finding the Stationary Values

• 12.2-1 Lagrange-multiplier method

• 12.2-2 Total-differential approach• 12.2-3 An interpretation of the

Lagrange multiplier• 12.2-4 n-variable and multi-

constraint case

Page 15: Ch. 12 Optimization with Equality Constraints

15

12.2-1 Lagrange-multiplier method

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Page 16: Ch. 12 Optimization with Equality Constraints

16

12.2-2 Total-differential approach

• dL = fxdx + fydy = 0 differential of L=f(x,y)

• dg = gxdx + gydy = 0 differential of g=g(x,y)

• dx & dy dependent on each other

• dy/dx = -fx/ fy slope of isoquant curve

• dy/dx = -gx/gy slope of the constraint line

• -gx /gy = -fx/ fy equal at the tangent

• fx/ gx = fy /gy = equi-marginal principle

Page 17: Ch. 12 Optimization with Equality Constraints

17

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Page 18: Ch. 12 Optimization with Equality Constraints

18

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Page 19: Ch. 12 Optimization with Equality Constraints

19

12.3 Second-Order Conditions

• 12.3-1 Second-order total differential

• 12.3-2 Second-order conditions• 12.3-3 The bordered Hessian• 12.3-4 n-variable case• 12.3-5 Multi-constraint case

Page 20: Ch. 12 Optimization with Equality Constraints

20

11.4 n-variable soc principal minors test for unconstrained max or min

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Page 21: Ch. 12 Optimization with Equality Constraints

21

12.3-1 Second-order total differential

has no effect on the value of Z* because the constraint equals zero but …

• A new set of second-order conditions are needed

• The constraint changes the criterion for a relative max. or min.

Page 22: Ch. 12 Optimization with Equality Constraints

22

12.3-1 Second-order total differential

0h β 2 iff 0)5(

h β 2)4(

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Page 23: Ch. 12 Optimization with Equality Constraints

23

12.3-1 Second-order total differential

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iff

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Page 24: Ch. 12 Optimization with Equality Constraints

24

361 p. W,&C;

0

H;

0

H

Where

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max(:definite negative0)1,...(0,0,0H

361) (p. soc, case variablend)

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soc of test variable3c)

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constraint than variablemore one

bemust therebecause test variable-one No a)

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Page 25: Ch. 12 Optimization with Equality Constraints

25

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Page 26: Ch. 12 Optimization with Equality Constraints

26

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Page 27: Ch. 12 Optimization with Equality Constraints

27

12.4 Quasi-concavity and Quasi-convexity

• 12.4-1 Geometric characterization• 12.4-2 Algebraic definition• 12.4-3 Differentiable functions• 12.4-4 A further look at the

bordered Hessian• 12.4-5 Absolute vs. relative

extrema

Page 28: Ch. 12 Optimization with Equality Constraints

28

12.5 Utility Maximization and

Consumer Demand • 12.5-1 First-order condition• 12.5-2 Second-order condition• 12.5-3 Comparative-static analysis• 12.5-4 Proportionate changes in

prices and income

Page 29: Ch. 12 Optimization with Equality Constraints

29

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30

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Page 31: Ch. 12 Optimization with Equality Constraints

31

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Page 32: Ch. 12 Optimization with Equality Constraints

32

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Page 33: Ch. 12 Optimization with Equality Constraints

33

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34

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Page 35: Ch. 12 Optimization with Equality Constraints

35

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Page 38: Ch. 12 Optimization with Equality Constraints

38

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Page 39: Ch. 12 Optimization with Equality Constraints

39

Graph: Substitution and Income Effects

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Quantity Q1

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P0

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If the price of Q1 increases, then the change in demand equals the substitution effect (AB)and the income effect (BC).

Page 40: Ch. 12 Optimization with Equality Constraints

40

B

A

C

U1

U0

Quantity X

Quantity Y

-Px1/Py0

If the price of Q1 increases, then the change in ordinary demand equals the sum of the substitution effect (AB) and the income effect (BC).

X1 X1' X0

Price X

P1

P0Ordinary demand

Compensated demand

Quantity X

-Px1/Py0 -Px0/Py0

Y1'Y0

Y1

Graph: Substitution and Income Effects

Page 41: Ch. 12 Optimization with Equality Constraints

52

12.7 Least-Cost Combination of Inputs

• 12.7-1 First-order condition• 12.7-2 Second-order condition• 12.7-3 The expansion path• 12.7-4 Homothetic functions• 12.7-5 Elasticity of substitution• 12.7-6 CES production function• 12.7-7 Cobb-Douglas function as a

special case of the CES function

Page 42: Ch. 12 Optimization with Equality Constraints

53

0

0

0

00,

,

0& ,, subject to Minimize

constant held are P & P where,,,;,,

conditionsorder -First 1-12.7

0

ba0

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baQQbPaPZ

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PPQbaZZ

Page 43: Ch. 12 Optimization with Equality Constraints

54

b

a

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a

b

a

b

ba

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a

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a

b

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linebudget and constraintBudget

onsubstituti technicalof rate marginal

Isoquant0

,

function Production

conditionsorder -First 17.12

0

0

0

Page 44: Ch. 12 Optimization with Equality Constraints

55

b

abbaba

b

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isfunction production The

341)-338 pp. 6, example (see conditionsorder -Second 2-12.7

Page 45: Ch. 12 Optimization with Equality Constraints

56

02

0

0 and 0such that

02

(max) definite negative ,021

1

1

341)-338 pp. 6, example (see ,conditionsorder -Second 2-12.7

22

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Page 46: Ch. 12 Optimization with Equality Constraints

57

02

0

isoquant convex strictly i.e., positive, ,0

min. definite) (positive negative ,0 and 0such that

02

negative ,01

21

inputs ofn combinatiocost Least 17.12

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Page 47: Ch. 12 Optimization with Equality Constraints

64

ρ-ρρ

ρ-ρρρρρ-ρρ

L-δKδjAjLjKQ

L-δKδjAjL-δjKδA11

111

1-

1-1

1,;11

11

scale toreturnsconstant i.e., one, degree of shomogeneou is CES

substition of elasticity determinesthat parameter on substituti theis

sharesfactor relative indicatingparameter on distributi theis

y technologof state theindicatingparameter efficiency theisA

00;-10 0;A where)L-(1KAQ

)63.12()L-(1KAQ

)L-(1KAQ

yhomogeneit of degree its find function, production CES aGiven

12.7-6 CES production function

Page 48: Ch. 12 Optimization with Equality Constraints

65

12.7-6 CES production function

111

111

111

-111

1-

1

1

)L-(1K where11

substition of elasticity determinesthat parameter on substituti theis

sharesfactor relative indicatingparameter on distributi theis

y technologof state theindicatingparameter efficiency theisA

01;-10 0;A where)L-(1KAQ

conditionsorder -first its find function, production CES aGiven

KA

KAQ

LA

LAQ

K

L

Page 49: Ch. 12 Optimization with Equality Constraints

66

12.7-6 CES production function

p.398) (12.66,0)1(

1

p.339) (11.40,

)L-(1K where 1

substition of elasticity determinesthat parameter on substituti theis

sharesfactor relative indicatingparameter on distributi theis

y technologof state theindicatingparameter efficiency theisA

01;-10 0;A where)L-(1KAQ

isoquant its of derivative1st thefind function, production CES aGiven

1

111

111

111

-111

1-

L

K

Q

Q

dL

dK

KA

LA

Q

Q

dL

dK

Q

Q

da

db

KAQ

LAQ

K

L

K

L

b

a

K

L

Page 50: Ch. 12 Optimization with Equality Constraints

67

convexLK

LKLK

LKdL

d

L

K

dL

d

dL

Kd

L

K

Q

Q

dL

dK

.dL

Kd

K

L

0)1(

)1(

)1()1(

)1()1(

)1()1(

)66.12(0)1(

0 function, CES theofisoquant an on that,Show

47.12

)2(1

)2(11)1(1

)1(11

2

2

1

2

2

12.7-6 CES production function

Page 51: Ch. 12 Optimization with Equality Constraints

68

12.7-6 CES production function

11111111

11

1

1-

1c where

1

1,

)1(

p.398) (12.66,0)1(

p.339) 11.40,&(11.39

substition of elasticity determinesthat parameter on substituti theis

sharesfactor relative indicatingparameter on distributi theis

y technologof state theindicatingparameter efficiency theisA

01;-10 0;A where)L-(1KAQ

onsubstituti of elasticity thefind function, production CES aGiven

b

a

b

a

b

a

b

a

K

L

b

a

b

a

P

Pc

P

P

L

K

P

P

L

K

P

P

L

K

L

K

Q

Q

dL

dK

P

P

Q

Q

da

db

Page 52: Ch. 12 Optimization with Equality Constraints

69

12.7-6 CES production function

1then ,0 if 1;then ,0 if 1;then ,01- if

p.399 12.68,1

1

ln

ln

ln11lnln

p.398 12.67,1

c where

substition of elasticity determinesthat parameter on substituti theis

sharesfactor relative indicatingparameter on distributi theis

y technologof state theindicatingparameter efficiency theisA

01;-10 0;A where)L-(1KAQ

easy way on,substituti of elasticity thefind function, production CES aGiven

1111

1-

K

L

K

L

K

L

PP

d

LK

d

P

Pc

L

K

P

Pc

L

K

Page 53: Ch. 12 Optimization with Equality Constraints

70

12.7-6 CES production function

1then ,0 if 1;then ,0 if 1;then ,01- if

p.399 12.68,1

1

1ln

ln

1

1

ln

ln

ln111

ln11ln

p.398 12.67, 1

substition of elasticity determinesthat parameter on substituti theis

sharesfactor relative indicatingparameter on distributi theis

y technologof state theindicatingparameter efficiency theisA

01;-10 0;A where)L-(1KAQ

easy way on,substituti of elasticity thefind function, production CES aGiven

1111

1-

LK

PP

LK

P

P

L

K

P

P

L

K

K

L

L

K

L

K

K

LP

P

L

K

K

L

K

L

Page 54: Ch. 12 Optimization with Equality Constraints

71

12.7-6 CES production function

1

11

////

/

/

1/

/

1c where

substition of elasticity determinesthat parameter on substituti theis

sharesfactor relative indicatingparameter on distributi theis

y technologof state theindicatingparameter efficiency theisA

01;-10 0;A where)L-(1KAQ

wayhard on,substituti of elasticity thefind function, production CES aGiven

111

111

111111

1111

1-

K

L

K

L

KL

KL

K

L

KLK

L

KL

K

L

PP

c

PPc

PPLKPPdLKd

P

Pc

PP

LK

P

Pc

PPd

LKd

P

Pc

L

K