Machine Learning lesson 12 http://v.163.com/movie/2008/1/O/T/M6SGF6VB4_M6SGKGMOT.html
1. clustering
2. k-means clustering algorithm
K-means算法是很典型的基于距离的聚类算法，采用距离作为相似性的评价指标，即认为两个对象的距离越近，其相似度就越大。
3. density estimation
anomaly detection or standout analysis
4. EM algorithm
这种方法可以广泛地应用于处理缺损数据，截尾数据，带有噪声等所谓的不完全数据(incomplete data)
see more inhttp://baike.baidu.com/view/1541707.htm
Gaussian discriminant Analysis
maximum likeliness estimation
Jensen's inequality:
In the context of probability theory,it is generally stated in the following form: if X is a random variable and f is a convex function,then f(EX) <= E(f(X)).