一个BP神经网络封装类。包括矩阵运算的封装。采用特殊封装方式，极大简化书写矩阵运算表达式，同时尽量减少申请/释放内存，提高运行速度。经过封装，这个神经网络结构很简单，易于理解，易于扩展。相信这个封装能给学习，应用神经网络的同学以方便。-A BP neural network package. Including a Matrix operations packaging. With special package methou, It greatly simplify the expression of matrix operations, while minimizing the allocating and releasing memory, and improve code speed. With this package, the neural network structure is very simple, easy-to-understand, easy to extend.