The function graph_tool.spectral.adjacency<http://graph-tool.skewed.de/static/doc/spectral.html?highlight=adjacency#graph_tool.spectral.adjacency> returns transpose of the adjacency matrix of a directed graph that is commonly used. Is this intentional? A misinterpretation of column-major versus row-major on my part? Compare a few standard examples: http://en.wikipedia.org/wiki/Adjacency_matrix#Examples http://www.math.cornell.edu/~mec/Winter2009/RalucaRemus/Lecture2/lecture2.ht... with the output of gt.adjacency(): import graph_tool.all as gt g = gt.Graph() v0 = g.add_vertex() v1 = g.add_vertex() e01 = g.add_edge(v0,v1) A = gt.adjacency(g) A.todense() [e for e in g.edges()] ## -- End pasted text -- Out[2]: [<Edge object with source '0' and target '1' at 0x11fb10d60>] A.todense() Out[3]: matrix([[ 0., 0.], [ 1., 0.]]) A in this case is most commonly defined as [[0, 1], [0, 0]]