catch-up effect 即追赶效应指其他条件相同，一开始贫穷的的国家和一开始富裕的国家在储蓄率相等的情况下，一开始贫穷国家的增长有更高的增长率，可是如何用数学公式证明呢？？附问题原文：Other things the same, a country with low income per person can have a higher growth rate than a country with a high income per person even if the countries have identical saving rates. Try to use equations to explain your answers.
我知道原因是报酬递减，但感觉无法用数学公式证明，求大神帮忙，谢谢！！