文章链接:http://mp.weixin.qq.com/s?__biz=MzIxMjAzNDY5Mg==&mid=2650791018&idx=1&sn=562df42ac2b0ce2bd62936a036cc812d&chksm=8f474981b830c097b901526cd87fb5d7b986d9f8a5f0daedf9470dbe379c4921d5bb6a545bbc&scene=21#wechat_redirect 原文: https://hit-scir.gitbooks.io/neural-networks-and-deep-learning-zh_cn/content/chap6/c6s6.html