介绍里面会用到MATHTYPE书写公式，比较麻烦。就直接给你贴了张图。有用的话，给个好评啊，呵呵...

[1]Fisher, L. & R. Weil, 1971, Coping with the Risk of Interest rate Fluctuations: Returns to Bondholders from Naive and OptimalStrategies [J], The Journal of Business44(4), 408-431.