According to the definitions, the differece between long-run and short-run is: in the short run there must be some fixed factor that can not be changed.

Hence, in the short run, the fixed cost can not be avoid, or we can call it the sunk cost, as long as price is higher than AVC, to run the factory is better than to close it.
max Pi=P*Q-C(Q)-FC, the production interval is [0,Qx], where P=MC(Qx)

In the long run seems every thing can be changed, we can choose a point p=LMC&p>LAC to run the factory if the point exists, if not close it.

[此贴子已经被作者于2006-6-29 21:18:00编辑过]