An Analytic Approximation for the American Put Price for Options on Stocks with Dividends
改进了Johnson的美式看跌期权近似公式，使其适用于在到期前有一次除息日的股票，并将近似值与Geske和Johnson的解析解对比，结果非常接近。
In a recent paper, Johnson [7] has given an analytic approximation to the American put price that delivers values that are very close to numerical solutions. The limitation to the Johnson approximation is that it is only applicable to put options on stocks without cash dividends. This study modifies the Johnson approximation to value options on stocks that have one exdividend date prior to the option expiration date, and these approximation values are compared to the analytic solutions provided by the Geske and Johnson [6] American put option pricing model. The approximation values are generally very close to the analytic solutions.