PCA

1.what's the PCA:

　　　From Wikipedia：Principal component analysis (PCA) is a statistical procedure that uses an orthogonal transformation to convert a set of observations of possibly correlated variables (entities each of which takes on various numerical values) into a set of values of linearly uncorrelated variables called principal components.link:https://en.wikipedia.org/wiki/Principal_component_analysis

2.what's function of PCA:

　　<1>.一个非监督学习的算法

　　<2>.主要用于数据降维

　　<3>. 通过降维， 可以发现人类更加容易理解的特征

　　<其他功能>. 可视化，去除噪音