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## Re: [igraph] Circular Reingold Tilford on tree is not planar!?

 From: Gábor Csárdi Subject: Re: [igraph] Circular Reingold Tilford on tree is not planar!? Date: Mon, 27 Jun 2011 11:45:55 -0400

```Actually, the graph that Tamas wrote is not a tree. I am still not
convinced that you can have a graph for which the non-circular layout
is planar, and the (properly converted) circular one is not.

Gabor

On Mon, Jun 27, 2011 at 11:08 AM, Robert Belleman <address@hidden> wrote:
> Hi Gabor, Tamás,
>
>
> So it is not possible to derive a circular planar layout from the
> RT layout?
>
> Because surely it must be possible to construct a planar circular
> layout for any tree?
>
> Do you know an alternative?
>
> Thanks,
> -- Rob
>
> Tamás Nepusz wrote:
>>
>>> it should be planar, AFAIK. If it is not planar, that means that the
>>> original non-circular one is not planar
>>
>> No, it isn't necesarily planar. A while ago I found a graph for which
>> the RT layout was planar but the circular RT layout wasn't, and I also
>> thought it was a bug, but it isn't. Try this graph for instance (given
>> as an edge list):
>>
>> 0-1, 0-2, 0-3, 0-4, 0-5, 0-6, 0-7, 0-8, 0-9, 4-10, 9-10
>>
>> When you use vertex 0 as root, the RT layout is planar but the circular
>> RT layout isn't.
>>
>> --
>> T.
>>
>>> , the circular one is just the
>>> transformation of that. Can you send us (in private if it's big, to
>>> Tamas and me) an example? I think this is a bug.
>>>
>>> Best,
>>> Gabor
>>>
>>> On Fri, Jun 24, 2011 at 9:55 AM, Robert Belleman <address@hidden
>>>>
>>>> Hi,
>>>>
>>>> I am applying the circular Reingold Tilford layout algorithm on a tree
>>>> consisting of 23k nodes and the same number of edges. I was expecting
>>>> this
>>>> algorithm to produce a planar layout but it doesn't.
>>>>
>>>> Can anybody enlighten me?
>>>>
>>>> Thanks,
>>>> -- Rob
>>>>
>>>> --
>>>> Robert Belleman, PhD, Computational Science, Faculty of Science
>>>> Universiteit van Amsterdam, Science Park 904, 1098 XH Amsterdam
>>>> The Netherlands. T: +31 20 525 7272/7463 F: +31 20 525 7490
>>>>
>>>> _______________________________________________
>>>> igraph-help mailing list
>>>> https://lists.nongnu.org/mailman/listinfo/igraph-help
>>>
>>>
>>>
>>> --
>>> KFKI RMKI
>>>
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>>
>>
>>
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--
Gabor Csardi <address@hidden>     MTA KFKI RMKI

```