Fig. 2

Adjacency sparsity plots and core–periphery profile of the Enron email dataset. The two panels in the top and the panel in the bottom-left corner show the nonzero entries of the adjacency matrix of the network, with different color intensities for different edge weights, when the nodes are re-labeled in three different ways: the top-left panel corresponds to the original node labeling; the top-right panel is the labeling obtained by re–ordering the nodes according to decreasing values of the overall degree d ̱ⁱⁿ+d ̱^out; the bottom-left is the labeling corresponding to decreasing values of the core–score computed with the proposed NSM. Finally, the bottom-right panel shows the persistence probability γ(S_k) as a function of k, when S_k is the set of the k most peripheral nodes according to the degree vector (orange line) or the NSM (blue line)