http://www.cnblogs.com/Deep-Learning/p/7073744.html

http://www.cnblogs.com/lutingting/p/4768882.html

http://chenrudan.github.io/blog/2016/01/09/logisticregression.html

http://www.cnblogs.com/Determined22/p/6362951.html

Softmax回归推到过程