#7184: [with patch, needs work] Implement counting of spanning trees for graphs
and digraphs + some fixing in kirchhoff_matrix
----------------------------+-----------------------------------------------
Reporter: AJonsson | Owner: rlm
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-4.2
Component: graph theory | Keywords:
Work_issues: | Author:
Reviewer: | Merged:
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Comment(by boothby):
Ncohen, you've broken kirchhoff_matrix. According to the definition, row-
sums of the Kirchhoff matrix should be zero. Here's the doctest before
you changed it:
{{{
sage: G = DiGraph({1:{1:2,2:3}, 2:{1:4}}, weighted=True,sparse=True)
sage: G.laplacian_matrix()
[ 3 -3]
[-4 4]
}}}
here, the row-sums are zero.
But you actually had to change the doctest to make the code pass,
{{{
sage: G = DiGraph({1:{1:2,2:3}, 2:{1:4}}, weighted=True,sparse=True)
sage: G.laplacian_matrix()
[ 4 -3]
[-4 3]
}}}
but the row-sums aren't zero! Don't break math to make code work!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7184#comment:5>
Sage <http://www.sagemath.org>
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