(2002) proceed by dropping the constraint that h ik be either 0 or 1/ v ∈A k d , but keeping the orthonormality constraint.
they seek to solve the following problem: By setting T := D 1/2 H, this can be rewritten as This problem is tractable because it is equivalent to the problem of finding the first K eigenvectors of D −1/2 LD −1/2 .