（精）高级微观经济课件.ppt

* his optimal p is such that D(p) S, that is, there are vacant apartments. * * * * 三棱锥 * 两种商品的假设比你起初想象的要更有概括性。因为我们常常把其中的一种商品看作是代表消费者要消费的一切东西。 举个例子，如果我们有兴趣研究消费者对牛奶的需求，我们会用xl来衡量他或她每月消费的牛奶夸脱数。于是我们可以让x2来代表消费者除了牛奶之外可能要消费的其他一切东西。 当我们采纳了这个解释后，就可方便地把商品2看作是消费者可以用来购买其他商品的货币。根据这种解释，商品2的价格自然而然是1，因为l美元的价格就是1美元。于是，预算约束的公式可以写为： p1x1+x2≤m (2．2) 这个公式简单地表明花费在商品1上的货币数量p1x1加上花费在共他商品上的货币数量不能大于消费者需要花费的货币总数m。 我们认为商品2代表了一种复合商品，它代表了消费者除了商品l之外还需要消费的共他一切东西。 * The budget constraint and budget set depend upon prices and income. What happens as prices or income change? No original choice is lost and new choices are added when income increases, so higher income cannot make a consumer worse off. * What happens if just one price decreases?Suppose p1 decreases How do the budget set and budget constraint change as p1 decreases from p1’ to p1”? Reducing the price of one commodity pivots the constraint outward. No old choice is lost and new choices are added, so reducing one price cannot make the consumer worse off. * Food stamps are coupons that can be legally exchanged only for food. How does a commodity-specific gift such as a food stamp alter a family’s budget constraint? F + G = 100; before stamps. Budget set after 40 food tamps issued. The family’s budget set is enlarged. * F + G = 100: before stamps. Budget constraint after 40 food stamps issued. What if food stamps can be traded on a black market for $0.50 each? Black market trading makes the budget set larger again. * Can be equivalently expressed as * But what if prices are not constants? E.g. bulk buying discounts, or price penalties for buying “too much”. Then constraints will be curved. Suppose p2 is constant at $1 but that p1=$2 for 0 - 20 and p1=$1 for x120. * Commodity 1 is stinky garbage. You are paid $2 per unit to accept it; i.e. p1 = - $2. p2 = $1. Income, other than from accepting commodity 1, is m = $10. Then the constraint is - 2x1 + x2 = 10 or x2 = 2x1 + 10. * More General Choice Sets Choi