文章链接:http://mp.weixin.qq.com/s?__biz=MzIxMjAzNDY5Mg==&mid=2650790973&idx=1&sn=9b7a5ff18afaf01687e550033a80575c&chksm=8f4749d6b830c0c03811873a7009273f62170277d2f63d27eb89bc3591529858a440a7b9b776&scene=21#wechat_redirect 原文: https://hit-scir.gitbooks.io/neural-networks-and-deep-learning-zh_cn/content/chap6/c6s5.html