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EdgeRenderingFunction to produce edge labels in GraphPlot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87549] EdgeRenderingFunction to produce edge labels in GraphPlot
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sat, 12 Apr 2008 07:03:16 -0400 (EDT)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • Reply-to: murray at math.umass.edu

I'm having trouble fathoming from the documentation how 
EdgeRenderingFunction works.  In a display produced by GraphPlot, 
applied to a graph that's a Graph object created with Combinatorica,  I 
want to be able to put distinct labels on the edges.

For example, take something very simple:

   g = Cycle[3];

I'd like to put labels "a", "b", "c" on the three {1,2}, {2,3}, {3,1}, 
respectively.

Here's what I tried finally:

   labels = Characters["abc"];
   edgeLabelFunction[{u_, v_}] :=
     labels[[First@Flatten@Position[Edges[Cycle[3]], {u, v}]]]

   offset={0.05,0.05}; (* to move labels away from edges *)

   GraphPlot[g, Method -> None,
     EdgeRenderingFunction -> ({
          Line[#1],
          Inset[edgeLabelFunction[#2], Mean[#1] + offset]
        ]} &)
   ]

This does not work.  How, exactly, do I index into the list of edges...

     Edges[g]
   {{1,2},{2,3},{1,3}}

.. so as to select the labels.  From the reference page on 
EdgeRenderingFunction, it seems to me that argument #2 is supposed to be 
the length 2 list {u,v} of vertices with which the edge is incident.

-- 
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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