说明：  有遗忘因子的最小二乘，递推最小二乘的缺点是常常出现数据饱和，新加入的数据对参数向量的更新作用不大，加如遗忘因子可很好的解决这一问题
(Forgetting factor least squares, recursive least squares drawback is often saturated data, new data on the update of the parameter vector, such as the forgotten factor can be a good solution to this problem)