说明：  此时例是关于用matlab实现牛顿法求解非线性方程组，（包含牛顿法、改进的牛顿法.梯度法、最速下降法代码），里面附带可以直接运行的程序。
(At this case is about solving nonlinear equations using matlab Newton, (including Newton, Newton method to improve the code), which comes with the program can be run directly.)