On 2013-04-17, Tom Boothby tomas.boot...@gmail.com 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
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
I've always
That might not have been terribly clear -- the point is, incidence
of edges and vertices is a binary relation. One needs to make a
choice to orient the matrix to make the linear algebra coincidence
work out.
On Mon, Apr 22, 2013 at 8:51 AM, Tom Boothby tomas.boot...@gmail.com wrote:
Yes it
On 2013-04-17, Michael Welsh yom...@yomcat.geek.nz wrote:
I have some GF(2) matrices that are incidence matrices of undirected graphs.
When I try to construct the graphs in sage, this happens:
sage: Graph(matrix(GF(2), [[1,0,1,1],[1,1,0,1],[0,1,1,0]]))
it's not even clear what two parallel
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
