PCA算法实现对数据降维，train_sample为训练样本，train_class为训练样本的分类结果，test_sample为测试样本，test_class为测试样本的分类结果，可以从UCI下载数据集进行调用~-PCA algorithm for data dimensionality reduction, train_sample of training samples, train_class for the classification of training samples, test_sample of test samples, test_class for the classification results of the test samples can be called from UCI download data sets ~