#5171: Bugs in the Graph constructor when input an adjacency matrix.
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Reporter: was | Owner: rlm
Type: defect | Status: new
Priority: critical | Milestone: sage-3.3
Component: graph theory | Keywords:
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1. The adjacency matrix of a graph constructed from an adjacency matrix
should either be the same or one should get an error when constructing the
graph:
{{{
sage: a = matrix(2,2,[1,0,0,1])
sage: Graph(a)
Graph on 2 vertices
sage: Graph(a).adjacency_matrix() # I think Graph(a) should work or given
an error
[0 0]
[0 0]
sage: Graph(a, loops=True).adjacency_matrix()
[1 0]
[0 1]
}}}
Another example -- this is WRONG, since multiple loops should not be
ignored.
{{{
sage: a = matrix(2,2,[2,0,0,1])
sage: Graph(a,loops=True).adjacency_matrix()
[1 0]
[0 1]
}}}
Why not just make a graph with loops and multiple edges (or at least
weighted edges) if and only if the adjacency matrix has diagonal entries
or non-1 entries? I'm guessing the Graph constructor just grew from a
time when these constructions weren't allowed or that networkx is just
poorly designed. Either way, this needs to be fixed for Sage.
2. When the input matrix is non-square, the error message is wrong in
multiple ways:
{{{
sage: a = matrix([1,0,0,1])
sage: Graph(a)
Traceback (most recent call last):
...
AttributeError: Incidence Matrix must have one 1 and one -1 per column.
}}}
* it should be "adjacency matrix".
* The exception should be ValueError, not AttributeError
* The Graph constructor doesn't take only 1's or -1's as input (but see
above)
* The Graph constructor is perfectly fine with having multiple 1's per
column!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5171>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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