We denote g(•) as the feature grouping function, which maps V original features to K groups, and a u k , b u k and c u k as the scaling, shifting and rotation operations over w s in group k for user u.
in addition, rotation is only performed for the features in the same group, and it is assumed to be symmetric, i.e., c u k,ij = c u k,ji , where g(i) = k and g(j) = k. the personalized classification model f u (x) after adaptation can be written as, wherew s = (w s , 1) to accommodate the shifting operation.