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Re: Re: changing style of vertices for ShowGraph with Combinatorica

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86347] Re: [mg86307] Re: changing style of vertices for ShowGraph with Combinatorica
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sun, 9 Mar 2008 05:00:56 -0500 (EST)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <fqqrql$k9j$1@smc.vnet.net> <200803081040.FAA13262@smc.vnet.net>
  • Reply-to: murray at math.umass.edu

So far so good, but this raises lots of questions:

(1) Why Text[#2,#1] in the pure function for VertexRenderingFunction? 
(Except that an example appears in the Documentation Center where this 
is used.  To what do the arguments refer?

(2) What about edge labeling?  If I specify a graph directly like this...

   g = {{1 -> 2, "a"}, {2 -> 3, "b"}, {3 -> 1, "c"}};

... then I can produce (and even PARTIALLY format) labels for it as follows:

   GraphPlot[g,
  VertexRenderingFunction -> ({EdgeForm[{Thick, Red}],
      FaceForm[Yellow], Disk[#1, 0.05], Text[#2, #1]} &),
  EdgeLabeling -> True, BaseStyle -> {FontSize -> 18}]

I said "partially" because, for example, I cannot change the font color 
in that BaseStyle specification.  And the edge labels are superimposed 
upon (i.e., inset into) the edge lines.  I can imagine providing an 
EdgeRenderingFunction to change that, but it seems like it would be 
rather complicated.

To do the same sort of thing with a But how do I do the same thing for a 
Combinatorica-type Graph object?  For example:

   g=Cycle[3]

I thought perhaps that using SetGraphOptions or this g might help, but 
the documentation for SetGraphOptions is almost useless.  Despite that 
documentation, I could get the following to work:

    g = Cycle[3];
    g = SetGraphOptions[g,
      {{{1,2}, EdgeLabel->"a"}, {{2,3},EdgeLabel->"b"},
       {{3,1}, EdgeLabel->"c"}}]
    ShowGraph[g]

However, using GraphPlot instead displays no edge labels with this:

   GraphPlot[g,
     VertexRenderingFunction -> ({EdgeForm[{Thick, Red}],
         FaceForm[Yellow], Disk[#1, 0.05], Text[#2, #1]} &),
     EdgeLabeling -> True]

And I am at a loss as to how to use EdgeRenderingFunction to display the 
edge labels I specified in the SetGraphOptions.  The documentation is 
just so horribly inadequate (at least for me) as to give no clue. 
Perhaps somebody else has a clue, or has managed to stumble upon this 
despite the non-documentation.

(3) And where, exactly, is all this documented carefully?  (I'm 
addressing this last question really to WRI!)  With GraphPlot, as with 
Combinatorica, the documentation is skimpy -- to be generous about the 
situation.

(I write all this from the standpoint of one who is trying to use 
Combinatorica's graph-theoretic functions for students who are relative 
Mathematica beginners.)

Steve Luttrell wrote:
> You could use the native GraphPlot function to plot your 
> Combinatorica-defined graph as follows:
> 
> Needs["Combinatorica`"]
> 
> g = Cycle[3];
> 
> GraphPlot[g,
>  VertexRenderingFunction -> ({EdgeForm[{Thick, Red}],
>      FaceForm[Yellow], Disk[#1, 0.05], Text[#2, #1]} &)]
> 
> Stephen Luttrell
> West Malvern, UK
> 
> "Murray Eisenberg" <murray at math.umass.edu> wrote in message 
> news:fqqrql$k9j$1 at smc.vnet.net...
>> With Mathematica 6, I can change the default style (medium black disk)
>> for rendering the vertices of a Combinatorica Graph like this:
>>
>>   Needs["Combinatorica`"]
>>
>>   g = Cycle[3];
>>   ShowGraph[g, VertexStyle -> Disk[Large], VertexColor -> Red]
>>
>> But how can I, for example, change the vertex style so it is, say, a
>> large yellow disk with a thick red boundary?  Or even just change it to
>> be a circle?  I tried "obvious" things like the following, but they
>> cause errors:
>>
>>   ShowGraph[g, VertexStyle -> Graphics[Circle[], ImageSize -> 20]]
>>
>> -- 
>> 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
>>
> 
> 

-- 
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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