davidp wrote:
> Sorry. I was not being clear. I was surprised by the fact that
> *only* the latter shows multiple edges.
>
> I am also surprised that arrowheads don't appear with multiple edges.
> This is especially a problem with weighted digraphs.
>
> (By the way, it probably would have been better for me to have written
>
> sage: G = DiGraph({1:{2: 2}, 2:{1:1}}, weighted=True)
>
> so that the Laplacian comes out correctly. However, this doesn't help
> with my problem.)
Well, the lack of arrowheads on weighted graphs is the problem in the
second case. Because the 0,1 entry is -1, Sage assumes that the matrix
represents a weighted graph.
Thanks,
Jason
>
> Dave
>
> On Mar 19, 6:01 pm, Jason Grout <[email protected]> wrote:
>> davidp wrote:
>>> Hi,
>>> I was a bit surprised by the difference exhibited below:
>>> sage: G = DiGraph({1:{2: 2}, 2:{1:1}})
>>> sage: G.show()
>> I'm surprised by the output of this. There are clearly two edges in the
>> graph: 1->2 and 2->1, but only one edge is shown.
>>
>>> sage: DiGraph(G.laplacian_matrix()).show()
>> The Laplacian matrix has nonzero entries indicating edges from each
>> vertex to each other vertex, so why do you find it surprising that there
>> are two edges?
>>
>> sage: H=DiGraph(G.laplacian_matrix())
>> sage: H.edges()
>> [(0, 0, 1), (0, 1, -1), (1, 0, -1), (1, 1, 1)]
>>
>> I find it surprising that arrowheads don't appear in the following, though:
>>
>> sage: DiGraph(G.laplacian_matrix()).show()
>>
>> Thanks,
>>
>> Jason
> >
>
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