logistic迴歸的損失函數以及向量化思想

轉自

http://www.javashuo.com/article/p-sizrpxzn-dr.html

 http://robinzheng.com/2015/08/13/%E9%80%BB%E8%BE%91%E5%9B%9E%E5%BD%92%E4%B8%8E%E8%AE%A1%E7%AE%97%E4%B8%AD%E7%9A%84%E5%90%91%E9%87%8F%E5%8C%96%E6%80%9D%E6%83%B3/

http://xuhongxu.com/ml7-logistic-regre-grad-desc/