Using relationships among the derivatives and Hessian matrices of the restricted and unrestricted
profit functions (discussed by Lau and others), long-run output and variable input demand function
and the associated elasticities can also be obtained. Using these elasticities, the long-run effects of
research as well as pricing and other government policies can be assessed. Empirical derivation of the
long-run results from an estimated short-run variable profit function is facilitated when specifying it to
be a normalized quadratic function. The advantage of this functional form is that closed-form
expressions can be derived for the optimal levels for the quasi-fixed factors. The quadratic
specification of the short-run profit function is:
∏ = во + Σα>i,Pl + ΣjμjZj+ Σ ад
+ 2 ΣΣιrWr + 2 ΣjΣ√jjZjZj∙ + 2 Σ k Σ kXkk WW (2)
+ Σ1Σjt4.P,Zi+ ΣΣ kΦ*PW + ΣjΣ MW
Taking the partial derivative with respect to output/ variable input prices (Hotelling’s Lemma) of
this profit function, the short-run output supply and variable input demand functions are then:
± Q =^∂∏ = αi+ Σiλp' + ΣηHZj+ ΣkφikWk i =1, . . . ., m,
(3)
Where the sign modifier of Qi is positive for an output supply equation and negative for a variable
input demand equation. Equations (1) are linear and can be solved readily for the Z*j. When capital
(j=K) and family labor (j=L) are assumed to be quasi-fixed, their optimal levels are:
K*
L*
γLL
-γLK
-γKL RK μK Σ iηiKPi Σ kθKkWk
Y-K J|_ RL — μL - Z^P — Σ θ W
(4)
where ∆ = γKKγLL — (γKL ) 2 . Defining the partial derivatives of the optimal capital and labor
equations as:
δKPI |
_д K * |
=— |
1 -TLLfLLKl- — YKL^iL ) |
i =1,.. |
, m |
δKWk |
≡ ∂ K * |
— |
∆ (Y∣LθKk — γKLθLk ) |
k=1,.. |
, S |
≡∂ Wk | |||||
δLPi |
∂L* д Pi |
1 |
(YKKηiL — YLKηiK ) |
i =1,. |
, m |
δLWk |
_ д L |
ɪ (γKKθLk — γLKθKk ) , |
k=1, |
, S | |
= ∂ W * |
The long-run output supply and variable input demand functions can be expressed as:
±Q* = α+Σ λ+ηδ + η7δ )p,+(μδ. + μδ )—δ R — δ. R
i i i' ii' i'k kpi i'l lpi i' k kpi l lpi kpi k lpi l
(5)
Σ (φ + θtδ + δδ,t W
k ik kk kwk lk lkk k
Note that equation (5) accounts for the additional impacts of prices on output and variable inputs
(price slopes are adjusted as compared to (3)) through capital and family labor adjustment. Moreover,