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Graph issue

  • To: mathgroup at
  • Subject: [mg101968] Graph issue
  • From: "Stuart Nettleton" <stuart.nettleton at>
  • Date: Fri, 24 Jul 2009 06:15:06 -0400 (EDT)

Hi friends, a change appears to have occurred in the behaviour of  
MakeGraph between Versions 6 and 7.01 (which has caused me some grief!)  
Below is a small example problem that produces the wrong answer in Version  
7.01.0, both 32bit and 64bit. A small topological sort I have included  
shows Combinatorica's topological sort also gives the wrong answer. Ant  
thoughts would be appreicated! Stuart

<< Combinatorica`
myverts1 = {a, b, c, h, d, e, f, g};
myedges1 = {{g, h}, {a, c}, {b, d}, {c, e}, {d, f}, {e, g}, {f, g}};
mygraph1 =
   MakeGraph[myverts1, (MemberQ[myedges1, {#1, #2}]) &,
    Type -> Directed, VertexLabel -> True];
Print["Before Edges: ", myedges1]
Print["After Edges: ", Map[myverts1[[#]] &, Edges[mygraph1]]]
Print["Before Leaves: ", {a, b}]
Print["After Leaves: ", Pick[myverts1, InDegree[mygraph1], 0]]
Print["Topological sort1: ", myverts1[[TopologicalSort[mygraph1]]]]

toposort = {}; nodes = myverts1;
visited = Table[False, {t, Length[nodes]}];
visit[n_] := Module[{},
    If[Pick[visited, nodes, n] == {False},
     visited[[Position[nodes, n][[1, 1]]]] = True;
      Cases[Map[Reverse, myedges1], {a_, b_} /; a == n][[All, 2]]];
     toposort = Append[toposort, n]
Map[visit, nodes];
Print["Topological sort2: ", toposort]

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