bring to market influences the market price. Thus the firm is not "faced with" any given price, and a more complicated model, e.g., a monopoly or oligopoly or differentiated-product model, should be used. Economists distinguish between the supply curve of an individual firm and the market supply curve. The market supply curve shows the total quantity supplied by all firms, so it is the sum of the quantities supplied by all suppliers at each potential price (that is, the individual firms' supply curves are added horizontally). Economists distinguish between short-run and long-run supply curve. Short run refers to a time period during which one or more inputs are fixed (typically physical capital), and the number of firms in the industry is also fixed (if it is a market supply curve). Long run refers to a time period during which new firms enter or existing firms exit and all inputs can be adjusted fully to any price change. Long-run supply curves are flatter than short-run counterparts (with quantity more sensitive to price, more elastic supply). Common determinants of supply are: Prices of inputs, including wages The technology used, Productivity Firms' expectations about future prices Number of suppliers (for a market supply curve) Demand schedule A demand schedule, depicted graphically as a demand curve, represents the amount of a certain good that buyers are willing and able to purchase at various prices, assuming all other determinants of demand are held constant, such as income, tastes and preferences, and the prices of substitute and complementary goods. According to the law of demand, the demand curve is always downward-sloping, meaning that as the price decreases, consumers will buy more of the good. Mathematically, a demand curve is represented by a demand function, giving the quantity demanded as a function of its price and as many other variables as desired to better explain quantity demanded. The two most common specifications are linear demand, e.g., the slanted line and the constant-elasticity demand function (also called isoelastic or log-log or loglinear demand function), e.g., the smooth curve which can be rewritten as Note that really a demand curve should be drawn with price on the horizontal x-axis, since it is the independent variable. Instead, price is put on the vertical, f(x) y-axis as a matter of unfortunate historical convention. Just as the supply curve parallels the marginal cost curve, the demand curve parallels marginal utility, measured in