中文说明：特征降维方法，其中包含有典型的特征组合方式——PCA和特征选择中的SFFS，SBS，SFS。共四类常用的特征降维方式。
English Description：
The feature dimension reduction method includes the typical feature combination methods PCA and SFFS, SBS, SFS in feature selection. There are four kinds of feature dimensionality reduction methods.