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Differential Models of Production: Change in the Marginal Cost and the Multi-Product Firm. Lecture XXVI. Change in the Marginal Cost. Shares of Marginal Cost Since both total and marginal cost depend on output levels and input prices, we start by considering marginal share of each input price.
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Differential Models of Production: Change in the Marginal Cost and the Multi-Product Firm Lecture XXVI
Change in the Marginal Cost • Shares of Marginal Cost • Since both total and marginal cost depend on output levels and input prices, we start by considering marginal share of each input price
Based on this definition, we define a Firsch price index for inputs as
Multiproduct Firm • Expanding the production function to a multiproduct technology
Expanding the preceding proof • Computing the first-order conditions
Now we replicate some of the steps from the preceding lecture, allowing for multiple outputs. • Taking the differential of the first-order condition with respect to each output
Differentiating with respect to the input prices yields the same result as before
Slightly changing the preceding derivation by differentiating the production function by a vector of output levels, holding prices and other outputs constant yields
Multiplying through by γyields • Using the tired first-order conditions
Differentiating the production function with respect to yields
Collecting these equations: • Differentiating the first-order conditions with respect to ln(z’) • Differentiating the first-order conditions with respect to ln(p’)
Differentiating the production function with respect to ln(z’) • Differentiating the production function with respect to ln(p’)
The extended form of the differential supply system is then. • Starting with the total derivative of ln(q) • Premultiplying by F
θir is the share of the ith input in the marginal cost of the rth product. • Summing this marginal cost over all inputs
Introduction of Quasi-Fixed Variables • Expanding the differential model further, we introduce quasi-fixed variables into the production set
Following Livanis and Moss, the differential supply function for this specification becomes
Starting with the input demand system, we add a random disturbance relying on the theory of rational random behavior (RRB, Theil 1975):