“…Projection of all data onto the subspace spanned by K columns of A, indexed by S, i.e., π S (A), can be expressed by a rank-K factorization, U V T . In this factorization, U ∈ R N ×K , V ∈ R M ×K , and U includes a set of K normalized columns of A, indexed by S. Therefore, the optimization problem (1) can be restated as [17]:…”