       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

```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;

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], {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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