On 2013-04-17, Tom Boothby <[email protected]> wrote: > Dima, > > Rows correspond to vertices and columns correspond to edges. This > matrix represents an undirected triangle with a double edge. I don't > understand why the graph __init__ requires a +1 and a -1 in each > column -- that describes a directed incidence matrix, and has no place > in undirected graphs. Yes it does, in a way. If you want to construct the Laplacian matrix L of the graph from the incidence matrix E just by using matrix multiplication, you need to pick up an orientation for each edge, i.e. assigning +1 to one end, and -1 to the other. Then, bingo, you have L=E.T*E
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