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Re: Using GraphPlot to draw an empty graph

  • To: mathgroup at smc.vnet.net
  • Subject: [mg105381] Re: [mg105358] Using GraphPlot to draw an empty graph
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Mon, 30 Nov 2009 06:11:42 -0500 (EST)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <200911291011.FAA16287@smc.vnet.net>
  • Reply-to: murray at math.umass.edu

You can finesse this by using the form

   GraphPlot[m]

where m is the adjacency matrix.  For example, for a 3-vertex null graph:

   GraphPlot[ConstantArray[0, {3, 3}]]


J. McKenzie Alexander wrote:
> Hello,
> 
> Is there a way of making GraphPlot draw an empty graph? I realise that 
> this is an ill-defined question if one uses the default options for 
> GraphPlot because there is no way for GraphPlot to know how many 
> vertices it should draw. However, it turns out that even if one set a 
> custom value for VertexCoordinateRule the vertices aren't drawn:
> 
> GraphPlot[{},
> VertexRenderingFunction -> ({Black, Disk[#1, 0.05] } &),
> VertexCoordinateRules ->
> Table[{Cos[theta], Sin[theta]}, {theta, 0, 2 Pi, 2 Pi/11}]
> ]
> 
> I know that I could easily draw this "by hand" using Graphics, but I 
> have good reason for wanting to use GraphPlot. (I wrap the GraphPlot in 
> Dynamic where the list of edges is specified by a variable. Most of the 
> time the variable contains a connected graph, but sometimes it is 
> empty.)
> 
> As an aside, the following "works" as a way of giving the impression of 
> an empty graph, but it does so by forcing each node to have a self-loop 
> (and then suppressing those edges from being drawn). It would be nice to 
> have a cleaner solution.
> 
> GraphPlot[Table[i -> i, {i, 0, 11}],
> VertexRenderingFunction -> ({Black, Disk[#1, 0.05]} &),
> SelfLoopStyle -> None,
> VertexCoordinateRules ->
> Table[N[{Cos[theta], Sin[theta]}], {theta, 0, 2 Pi, 2 Pi/11}]
> ]
> 
> Cheers,
> 
> Jason
> 
> --
> Dr J. McKenzie Alexander
> Department of Philosophy, Logic and Scientific Method
> London School of Economics and Political Science
> Houghton Street, London WC2A 2AE
> 
> 
> 
> 

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305


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