unified form of kernel pca

• PCA
  $\max_u u^T\tilde{X}\tilde{X^T}u \\ s.t. u^Tu=1$umax​uTX~XT~us.t.uTu=1
  $\tilde{X}=U\Sigma V^T$X~=UΣVT，$Y=U^TX$Y=UTX