说明：  最速下降法是一种沿着N维目标函数的负梯度方向搜索最小值的方法。该程序是用最速下降法求无约束最优化解。
(Steepest descent method is an N-dimensional objective function along the negative gradient direction of the minimum search method. The program is used steepest descent method for unconstrained optimal resolve.)