An adjacency matrix is a binary matrix A, such that A(i, j) = 1 if there is an edge from node i to node j, and 0 otherwise.

Here is an example:

adj =
     0     0     1     0     0
     0     0     1     1     1
     1     1     0     1     1
     1     1     1     0     1
     0     0     0     1     0