实现BP神经网络训练的小程序。采用单输入单输出的3层BP网络，神经网络隐层采用标准的sigmoidal激活函数，输出层采用线性激活函数。-BP neural network training procedures. Single-input single-output three-layer BP network, the neural network hidden layer using a standard sigmoidal activation function, the output layer uses linear activation function.