Supply (economics)
Supply function and equation

The supply function is the mathematical expression of the relationship between supply and those factors that affect the willingness and ability of a supplier to offer goods for sale. An example would be the curve implied by Q s = f (P; P rg) {\displaystyle Q_{\text{s}}=f(P;P_{\text{rg}})} where P {\displaystyle P} is the price of the good and P rg {\displaystyle P_{\text{rg}}} is the price of a related good. The semicolon means that the variables to the right are held constant when quantity supplied is plotted against the good's own price. The supply equation is the explicit mathematical expression of the functional relationship. A linear example is Q s = 325 + P − 30 P rg {\displaystyle Q_{\text{s}}=325+P-30P_{\text{rg}}} Here 325 {\displaystyle 325} is the repository of all non-specified factors that affect supply for the product. The coefficient of P {\displaystyle P} is positive following the general rule that price and quantity supplied are directly related. P rg {\displaystyle P_{\text{rg}}} is the price of a related good. Typically, its coefficient is negative because the related good is an input or a source of inputs.
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