中文说明：
用多层前向网络的BP算法拟合函数
1）网络结构为三层（输入层、1个隐层和输出层）；
2）获取两组数据，一组作为训练集，一组作为测试集；
3）用训练集训练网络；
4）用测试集检验训练结果。
English Description：
Fitting function with BP algorithm of multilayer feedforward network
1) The network structure consists of three layers (input layer, one hidden layer and output layer);
2) Two sets of data were obtained, one as training set and one as test set;
3) The network is trained by training set;
4) Test set was used to test the training results.