It is based on feature augmentation, incorporating explicit correlation into augmented feature spaces.
it expands baseline feature vector x to be Φ s (x) = (ρx, (1 − ρ 2 ) 1/2 x) and Φ t (x) = (x, 0 p ) for source and target domain data in R 2p respectively, with ρ being the correlation between source and target domain data.