说明：  Steffensen迭代法求非线性方程的根，和Steffensen加速迭代法求非线性方程的根做对比的例程，有详细中文注释。
(Steffensen iteration method for the nonlinear equations of the root, and Steffensen iteration method for the nonlinear equations to accelerate root to do comparison routine, detailed notes in Chinese.)