Editing Perfect competition (section)

==Short-run supply curve==
The short-run (<math>\text{SR}</math>) supply curve for a perfectly competitive firm is the marginal cost (<math>\text{MC}</math>) curve at and above the shutdown point. Portions of the marginal cost curve below the shutdown point are not part of the <math>\text{SR}</math> supply curve because the firm is not producing any positive quantity in that range. Technically the <math>\text{SR}</math> supply curve is a discontinuous function composed of the segment of the <math>\text{MC}</math> curve at and above minimum of the average variable cost curve and a segment that runs on the vertical axis from the origin to but not including a point at the height of the minimum average variable cost.<ref>Binger & Hoffman, ''Microeconomics with Calculus'', 2nd ed. (Addison-Wesley 1998) at 312–14. A firm's production function may display diminishing marginal returns at all production levels. In that case both the <math>\text{MC}</math> curve and the <math>\text{AVC}</math> curve would originate at the origin and there would be no minimum <math>\text{AVC}</math> (or min <math>\text{AVC} = 0</math>). Consequently, the entire <math>\text{MC}</math> curve would be the <math>\text{SR}</math> supply curve.</ref>