%PCA PRINCIPLE COMPONENTS ANALYSIS % X是n1*n2的,n1是变量个数,n2是样本数 % 返回值p是转换坐标系 N说明投影到N个坐标系上 % p*X 才是投影结果 % Performing principal components analysis on the N1-by-N2 real-valued % data matrix X, where N1 and N2 are the number of features (N1 变量个数) % and observations (N2 采样个数), respectively.