在实际课题中，为了全面分析问题，往往提出很多与此有关的变量(或因素)，因为每个变量都在不同程度上反映这个课题的某些信息。(PCAPrincipal Component Analysis (PCA) is a multivariate statistical analysis method that selects multiple variables by linear transformation to select fewer variables. It is also called principal component analysis.)