Preferred variable names

Common names include:

• adjacency for square adjacency matrices of graphs
• biadjacency for rectangular biadjacency matrices of bipartite graphs
• n = adjacency.shape[0] for the number of nodes of the graph under study
• n_row, n_col = biadjacency.shape for the number of nodes in each of the two sets of nodes of the bipartite graph under study.
• i (respectively j) should be preferred when iterating over the rows (respectively the columns) of some matrix.