Editing Marginal cost (section)

== Long run marginal cost ==
[[File:Long run marginal cost.png|thumb|Long Run Marginal Cost]]
[[Long_run_and_short_run|The long run]] is defined as the length of time in which no input is fixed. Everything, including building size and machinery, can be chosen optimally for the quantity of output that is desired. As a result, even if short-run marginal cost rises because of capacity constraints, long-run marginal cost can be constant. Or, there may be increasing or decreasing [[returns to scale]] if technological or management productivity changes with the quantity. Or, there may be both, as in the diagram at the right, in which the marginal cost first falls (increasing returns to scale) and then rises (decreasing returns to scale).<ref> The classic reference is Jakob Viner, "Cost Curves and Supply Curve", ''Zeitschrift fur Nationalokonomie'', 3:23–46 (1932).</ref>