中文说明：基于斯坦福大学机器学习公开课，matlab实现了Back propagation算法。代码中包含算法实现的整个过程：包括数据的提取、数据的图像演示、运行验证情况等。运行比较简单，只需要运行ex4.m即可，所有的功能都可实现。具体Back propagation算法的讲解过程可以斯坦福大学机器学习的公开课。
English Description：
Based on the machine learning classes at Stanford University, MATLAB Back propagation algorithm is implemented. Code contains an algorithm to implement the whole process: image presentations, including data extraction, data verification, and so on. Operation is relatively simple, only need to run EX4.m to, all the functions can be realized. Explaining the process of Back propagation algorithm machine learning seminar at Stanford University.