https://www.zhihu.com/question/23765351
http://blog.csdn.net/u013146742/article/details/51986575
http://www.cnblogs.com/neopenx/p/4453161.html
NN 激活函数 待修改
原文：http://www.cnblogs.com/squirrel2300/p/6876581.html
