机器学习中的正则是什么: https://www.zhihu.com/question/20924039/answer/131421690
Regularization and variable selection via the elastic net:
https://web.stanford.edu/~hastie/Papers/B67.2%20%282005%29%20301-320%20Zou%20&%20Hastie.pdf
高斯分布与L2正则: http://qwone.com/~jason/writing/l2gaussian.pdf
MLE;MAP;贝叶斯估计: https://zhuanlan.zhihu.com/p/37215276