Here, Y = [y1, y2,⋯,yn], F = [f1, f2,⋯,fn] ∈ Rn × C, H is an n × n diagonal matrix with Hii = 1 if i ≤ l, and Hii = 0 otherwise, L = (I - W )T (I - W) and I is an n × n identity matrix, tr(·) and T are the matrix trace and transpose operators, respectively. By taking the differentiation of Eq. (2) to F and setting the differentiation to zero, F can be computed as: