On Thu, Jan 15, 2009 at 11:30 AM, Vincent D <[email protected]> wrote:
>
> Hello,
>
> I'm in trouble with plotting multiedge Graphs because it seems that
> there is no method to specify that a plotted edge should be something
> else than a segment from one vertex to the other (except for loops).
> The result is that, if I had two edges from 1 to 2, I see just one
> edge from 1 to 2. Moreover, if I had label on each edge, the labels
> overwrite ! We can set the position of each vertex independently (with
> the set_pos method) but I didn't find how transform the edge-plotting
> method.
>
> A solution is to implement my own plotting method... but I think that
> there is just one thing to modify in the preexistent one.
>
> Could someone help me ?
>
> Thank you,
> Vincent

I don't have much to say, except this is a known and I think *very*
serious bug.    I would much rather plotting to fail than to silently
work and give wrong answers.  I really wish somebody would improve the
graph plotting code in Sage to give multiple edges (etc.) correctly.

This exact problem kept a Sage-created diagram from appearing in
Science (or Nature?) Magazine this month, where somebody had a paper
with an expander graph (of a Hecke operator) and had to make the plot
with GraphViz instead of sage because of this problem.  She had
complained to me about this...

So I strongly encourage you to do something about this, and can tell
you I think nobody else is working on it.   Regarding finding the
code, it's probably somewhere in
   SAGE_ROOT/devel/sage/sage/plot/
but I'm not sure.  You might try
   sage: search_src?


William

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