文章链接:http://mp.weixin.qq.com/s?__biz=MzIxMjAzNDY5Mg==&mid=2650790947&idx=1&sn=0b85ea3c4ec28fc577d18d4dbc2280a4&chksm=8f4749c8b830c0deeae0e9bd8ee84f807a380ffb4fa552d545d9955ca07e44bbabc0b629638b&scene=21#wechat_redirect 原文: https://hit-scir.gitbooks.io/neural-networks-and-deep-learning-zh_cn/content/chap6/c6s3.html