#15669: Errors with graph complement
-------------------------------------+-------------------------------------
Reporter: tscrim | Owner: tscrim
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.1
Component: graph theory | Resolution:
Keywords: | Merged in:
Authors: Travis Scrimshaw | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/graphs/complement-15699 | e2a498c3c7adc71adcadd76b0bc09ea9a6efe77c
Dependencies: | Stopgaps:
-------------------------------------+-------------------------------------
Changes (by {'newvalue': u'Travis Scrimshaw', 'oldvalue': ''}):
* status: new => needs_review
* commit: => e2a498c3c7adc71adcadd76b0bc09ea9a6efe77c
* branch: => public/graphs/complement-15699
* author: => Travis Scrimshaw
Old description:
> We can't take the complement of an immutable graph:
> {{{
> sage: Gamma = graphs.PathGraph(5).copy(immutable=True)
> sage: Gamma.complement()
> NotImplementedError
> }}}
> which is because `copy(Gamma)` doesn't return a mutable copy.
>
> They are plotting their original graph.
> {{{
> sage: G = graphs.PathGraph(5)
> sage: G.plot()
> sage: GC = G.complement()
> sage: GC.plot() # Same as G.plot()
> }}}
New description:
We can't take the complement of an immutable graph:
{{{
sage: Gamma = graphs.PathGraph(5).copy(immutable=True)
sage: Gamma.complement()
NotImplementedError
}}}
which is because `copy(Gamma)` doesn't return a mutable copy.
--
Comment:
Replying to [comment:1 ncohen]:
> Well, I guess you can fix this one yourself ! You should just add a
`immutable=True` to the call of `copy` in this method.
Done and NR. Although making an immutable copy destroys the name of the
graph, so a slightly different question is do we want that behavior.
> Besides, your second example of code is not really a bug. `GC` is what
it should be, but if you plot the complement of a graph with the same
layout as for the original graph, it so happens that the edges are all
horizontal too. You can add a `layout="spring"` to `plot()` to emphasize
it.
Ah, I see. I also understand why you want to keep the same layout as the
original graph too.
Thanks,[[BR]]
Travis
----
New commits:
||[http://git.sagemath.org/sage.git/commit/?id=5b42e196c7ad877732d84090c4c59c4d878f1888
5b42e19]||{{{Fixed complement for immutable graphs.}}}||
||[http://git.sagemath.org/sage.git/commit/?id=e2a498c3c7adc71adcadd76b0bc09ea9a6efe77c
e2a498c]||{{{Fixed doctest output.}}}||
--
Ticket URL: <http://trac.sagemath.org/ticket/15669#comment:2>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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