加载中…微观经济复习总结--cost function:Long-run and short-run cost curves
(2011-03-20 16:58:28)
标签：
longshortcostcurves微观经济 |
分类： 应用经济学_统计计量 |
It is clear that the long-run cost
curve must never
lie above any
short-run cost curve, since the
short-run cost minimization
problem
is just a constrained version
of the long-run cost
minimization
problem.
Let us write the long-run cost function as
c(y) = c(y, z(y)). Here we have
omitted the factor prices since they are
assumed fixed, and we let z(y)
be
the cost-minimizing demand for a single fixed factor. Let y*
be some given
level of output, and let
z* = z(y*) be the associated long-run demand
for
the fwed factor.
The short-run cost,
c(y, z*), must be
at least as
great
as the long-run cost, c(y, ~(y)),
for all levels of
output, and the
short-run
cost will equal the
long-run cost at output y*, so c(y*,
z*) = c(y*,
~(y*)).
Hence, the long- and the
short-run cost curves must be tangent at
y*.
This is just a geometric restatement of the
envelope theorem. The
slope
of the long-run cost curve at y*
is
http://s14/middle/7939a4adg9ee6543edf1d&690function:Long-run and short-run cost curves" TITLE="微观经济复习总结--cost function:Long-run and short-run cost curves" />
http://s14/middle/7939a4adg9ee6547bf47d&690function:Long-runand short-run cost curves" TITLE="微观经济复习总结--cost function:Long-run and short-run cost curves" />
http://s14/middle/7939a4adg9ee6547bf47d&690function:Long-run
Average cost curves:
The average variable cost curve
will
5.1 eventually rise with
output, while the average fixed
cost curve
always falls with output. The interaction
of these two
effects
produces a U-shaped average cost curve.
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