Re: [igraph] double headed and curving edges in tkplot

[Gabor Csardi]

On Sat, Mar 03, 2007 at 03:46:51PM -0800, Jarrett Byrnes wrote:
> A second question (apologies if this is a lot).  tkplot() seems to  
> allow for curved arrows when a vertex points to itself.

Correct. (But only in this case.)

> 1) Is there a way to make other edges bow or curve.  Specifically, I  
> have two vertexes, each with a directed path from one to the other.   
> I wish the user to be able to see these as two separate paths, and  
> hence want them to bow out a little bit.

No, there isn't a way currently. 

> 2) Can one make a double-headed edge?  What is the proper attribute  
> for this?

If you create both an A->B edge and a B->A one then the edge 
should be double-headed. (Actually two separated edges are drawn.

> 3) Can one have a graph both with double-headed edges and have  
> reciprocal edges as in 1) above?

As you can't have curved edges, i'm afraid that the answer to this 
question is no as well.

> Thanks!  I'm trying to sort through the documentation on attributes,  
> but it seems somewhat sparse.  This package is wonderful, though!   
> Thanks so much!

Thanks. You might want to check the 0.3.3 version, it is on CRAN now, 
i've corrected a bug in plot.igraph, so it can also draw loop edges.
There is also some code in it to draw Bezier curves, so it would be not
too difficult to add support for curved edges using it.

tcltk can also plot Bezier curves, so it is also not too hard to add
support for curved edges in tkplot. 

If you like Python, the Python interface can also plot curved edges,
see the igraph homepage for the link.

You might also want to check the SNA package, this can draw curved edges
and its plotting functions are more sophisticated in general. It uses 
adjacency matrices for data. 

I've added curved edge support in R to the TODO list, not that this
really means anything...

Please tell me if you've further questions, best,
Gabor

> -Jarrett
> 
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-- 
Csardi Gabor <address@hidden>    MTA RMKI, ELTE TTK