说明：  采用bp神经网络对函数y=sin（x）进行训练，然后用测试集对训练的函数进行测试，也就是函数逼近sin（x)的曲线
(Bp neural network using the function y = sin (x) for training, and then use the test set to test the training function, that is, function approximation sin (x) curve)