文章链接:http://mp.weixin.qq.com/s?__biz=MzIxMjAzNDY5Mg==&mid=2650790932&idx=1&sn=10c8c5ee729d1fa200d2dd189f5edc38&chksm=8f4749ffb830c0e9a0efb8a6f944ba49c3419c995d8a07885f30afd3a0743040b266b5751255&scene=21#wechat_redirect 原文: https://hit-scir.gitbooks.io/neural-networks-and-deep-learning-zh_cn/content/chap6/c6s2.html