用BP算法实现函数 逼近。

说明：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

-With BP algorithm function approximation. Descr iption: 1) The network structure of the three-layer (input layer, a hidden layer and output layer) 2) to obtain two sets of data, a set as the training set, a set as a test set 3) training network training set) using the test the set inspection training results