where d is a damping factor, N is the number of all nodes in the network, u is a in neighbour is the set of in neighbours of v, and d + (u) is the out degree of u. Explanations on the different types of degrees and neighbours are given in Section 2.1. The damping factor in the graph-tool implementation 54 is set to 0.85 and the default convergence limit of 1×10 -6 is used.