“…Typically, it is the ranking of the centrality values that matters-we only care whether one node is more or less important than another, so the vector x ∈ R N is equivalent to βx + γ1 for any β, γ > 0. We summarize here the concepts of Katz, eigenvector and degree centrality, refering to [1,6,12,25,29] for historical details and discussions of implementation issues. We also consider the PageRank algorithm [14,20,28] which has a different feel; summarizing incoming, rather than outgoing, information, but also assigns a positive real value to each node.…”