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Combinatorica`ShowGraph HeadCenter option

• To: mathgroup at smc.vnet.net
• Subject: [mg87107] Combinatorica`ShowGraph HeadCenter option
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Tue, 1 Apr 2008 03:20:33 -0500 (EST)
• Organization: Mathematics & Statistics, Univ. of Mass./Amherst
• Reply-to: murray at math.umass.edu

In whatever version of Mathematica was current 5 years ago, the 
following code displayed a directed graph with the arrows located 
half-way along each edge:

   <<DiscreteMath`Combinatorica`
   g = SetGraphOptions[Cykcle[3], EdgeDirection -> True];
   ShowGraph[g, HeadCenter -> 0.5]

In Mathematica 6.0.2 (with Combinatorica` instead of 
DiscreteMath`Combinatorica`, of course), the option HeadCenter seems to 
be unrecognized, and the arrows remain at their target ends -- in other 
words, they appear where they are hardest to see!

Has this change been documented?  There is nothing whatsoever about this 
in Compatibility/tutorial/DiscreteMath/Combinatorica.  Except that this 
compatibility guide states, "All of the functionality in 
DiscreteMath`Combinatorica` is available in the newly created 
Combinatorica Package."  Plainly that is not the case in so far as 
HeadCenter is concerned.

How can one still locate the arrows on the displayed directed graph -- 
using ShowGraph (which has been generally much simpler to use, 
especially for students, in contrast with the newer GraphPlot.

-- 
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