为什么自然垄断的平均总成本是递减的？边际成本是不随数量变化而变化的？ 有实例最好啦，求解释。。。。

在一个自然垄断不存在的行业中，绝大多数行业，边际成本随着规模经济而下降，随着公司成长的痛苦而增加。自然垄断的成本结构是非常不同的。自然垄断产品固定成本高,不依赖于输出,因为平均总成本=总成本(固定+可变成本)/总输出,远高于可变成本和固定成本,可变成本可以是可忽略不计的程度,所以这是一个很简单的数学题分子保持不变,分母增加,res

In an industry where a natural monopoly does not exist, the vast majority of industries, the marginal cost decreases with economies of scale, then increases as the company has growing pains. A natural monopoly has a very different cost structure. A natural monopoly has a high fixed cost for a product that does not depend on output, since average total cost = total cost(fixed+variable cost)/total output, and fixed cost is much higher than variable cost, to an extent which variable cost can be neglectable, so it's an easy math problem as numerator stays the same, denominator increases, the result decrease. For the same reason, the marginal cost is the change of total cost caused by producing one more unit of product, for example, you invest $1000 to produce condom, with one more production of condom, your cost increase $0.5. So no matter you produce how many condom, your marginal cost, the cost of producing one more, is always $0.5, while your average total cost changes dramatically. If you produce only one condom, the average cost is $1000.5, but if you produce 100,000, it drops to $0.51.