说明：  BP 神经网络是一种多层前馈神经网络，该网络的主要特点是信号前向传递，误差反向传播。在前向传递中，输入信号从输入层经隐含层逐层处理，直至输出层 ． 每一层的神经元状态只影响下一层神经元状态 。 如果输出层得不到期望输出，则转入反向传播 ，根据预测误差调整网络权值和阔值
(BP neural network is a multi-layer feedforward neural network. Its main characteristics are forward signal transmission and back error propagation. In forward transmission, the input signal is processed from the input layer through the hidden layer to the output layer. The state of neurons in each layer only affects the state of neurons in the next layer. If the output layer can't get the desired output, it goes back propagation and adjusts the network weights and broadband values according to the prediction error)