中文说明：
BP神经网络的仿真，能够拟合各种函数，支持梯度下降法和LM两种训练算法。所有代码自己编写，没有使用matlab自带的函数，是学习的最佳范本。
English Description：
BP neural network simulation, can fit a variety of functions, support gradient descent method and LM two kinds of training algorithm. All the code written by themselves, without the use of Matlab's own function, is the best model for learning.