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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
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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
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/ fyequal at the tangent • fx/ gx = fy /gy = equi-marginal principle
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
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/ fyequal at the tangent • fx/ gx = fy /gy = equi-marginal principle
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
11.4 n-variable soc principal minors test for unconstrained max or min
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.
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
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
Quantity Q2 P0 If the price of Q1 increases, then the change in demand equals the substitution effect (AB) and the income effect (BC). P0 B A C U0 U1 Quantity Q1 P1 P1 P0 Graph: Substitution and Income Effects
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). B Y1'Y0 Y1 A C U0 U1 -Px1/Py0 -Px0/Py0 Quantity X Price X P1 P0 Ordinary demand Compensated demand X1 X1' X0 Quantity X Graph: Substitution and Income Effects
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