en consider the special case of M(D), the set of adjacency matrices of graphs with fixed degree distribution D. Wedefine G(D) accordingly by switching negative checkerboardsin symmetric pairs. We show that Z2, an approximation ofthe spectral radius λ1 based on the second Zagreb index, isnon-decreasing along arcs of G(D). Also, λ1 reaches its maximum in M(D) at a sink of G(D). We provide simulation