For unweighted networks of N nodes without multiple connections, the network structure can be represented an N×N adjacency matrix A. Unfortunately, if the network is directed, there exist opposite conventions for how to define the adjacency matrix. In these pages, we will act like mathematicians and define the adjacency matrix so that the component aij indicates a connection from node j and to node i. In this convention, one must read the indices from right to left to determine the direction of the interaction. (Many people use the opposite convention where one must read the indices from left to right.) The adjacency matrix is a matrix of ones and zeros where a one indicates the presence of a connection. Therefore we define A by