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Re: FromAdjacencyMatrix / FromAdjacencyLists - broken?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg104379] Re: [mg104192] FromAdjacencyMatrix / FromAdjacencyLists - broken?
  • From: David Bevan <david.bevan at pb.com>
  • Date: Thu, 29 Oct 2009 02:59:49 -0500 (EST)

I see the problem (on 32-bit Windows).

Looking at the Combinatorica code, the problem seems to be in the call to
SetGraphOptions[g, EdgeDirection -> True] which apparently normalises the edge list by sorting if the source graph is undirected before making the result directed:

In[]:= g1=Cycle[3,Type->Directed];
In[]:= List@@g1
Out[]= {{{{1,2}},{{2,3}},{{3,1}}},{{{-0.5,0.866025}},{{-0.5,-0.866025}},{{1.,0}}},EdgeDirection->True}

In[]:= g2=SetGraphOptions[g1, EdgeDirection -> False];
In[]:= List@@g2
Out[]= {{{{1,2}},{{2,3}},{{3,1}}},{{{-0.5,0.866025}},{{-0.5,-0.866025}},{{1.,0}}},EdgeDirection->False}

In[]:= g3=SetGraphOptions[g2, EdgeDirection -> False];
In[]:= List@@g3
Out[]= {{{{1,2}},{{2,3}},{{1,3}}},{{{-0.5,0.866025}},{{-0.5,-0.866025}},{{1.,0}}},EdgeDirection->False}

Note that g3 is normalised, but g2 isn't.

FromAdjacencyMatrix should really create a directed graph directly.

I can't see why different endian-ness should affect this though.

David %^>


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