“…The solution taken by e.g., [33,29,4], which leads to the spectral method, is less combinatorial and more algebraic, less local and more global, and can be phrased as follows: Let us instead find a matrix H that 1) is easy to compute 2) has the same dimensions as H, but rank at most n, and 3) is "as close as possible" toĤ under some metric, with this rank constraint. One particular way of computing such H (among, perhaps, other possibilities) is the spectral method described next.…”