residual   翻译过来是剩余的  意思 我没看过你那教材 自己体会下看是什么意思

我知道是剩余的意思……
就是不知道这个计算还是什么的到底是怎么一回事……
虽然有公式~~但我觉得如何能得出那个公式……
只知道 residal supply curve 是跟贸易相关的~~

model with 2 firms and constant marginal cost.

p1 = firm 1 price, p2 = firm 2 price
q1 = firm 1 quantity, q2 = firm 2 quantity
c = marginal cost, identical for both firms
Equilibrium prices will be:

p1 = p2 = P(q1 + q2)
This implies that firm 1’s profit is given by Π1 = q1(P(q1 + q2) − c)

Calculate firm 1’s residual demand: Suppose firm 1 believes firm 2 is producing quantity q2. What is firm 1's optimal quantity? Consider the diagram 1. If firm 1 decides not to produce anything, then price is given by P(0 + q2) = P(q2). If firm 1 produces q1' then price is given by P(q1' + q2). More generally, for each quantity that firm 1 might decide to set, price is given by the curve d1(q2). The curve d1(q2) is called firm 1’s residual demand; it gives all possible combinations of firm 1’s quantity and price for a given value of q2.