直接上比较清晰的博文：
1. Logistic and Softmax: http://www.cnblogs.com/daniel-D/archive/2013/05/30/3109276.html
2. BP: http://www.cnblogs.com/daniel-D/archive/2013/06/03/3116278.html
3. Logistic regression：http://www.dreamingo.com:9999/blog/standford-note-logistic-regression
4. Softmax regression：http://www.cnblogs.com/bzjia-blog/p/3366780.html