Bug: Combinatorica Neighborhood doesn't do anything.
- To: mathgroup at smc.vnet.net
- Subject: [mg119188] Bug: Combinatorica Neighborhood doesn't do anything.
- From: BernieTheJet <berniethejet at gmail.com>
- Date: Tue, 24 May 2011 05:58:37 -0400 (EDT)
I am not sure what the relationship between Combinatorica and the
built in Mathematica functions is anymore. It seems a lot of Combinatorica
has been moved to the kernel. That being said, I believe there is no
kernel Neighborhood function for graphs yet, and if so, the one in
Combinatorica doesn't do much of anything:
So, for example, try:
GraphPlot[ nn = {1 -> 2, 1 -> 3, 2 -> 5, 2 -> 3, 3 -> 4, 4 -> 3, 3 ->
6, 5 -> 6}, VertexLabeling -> True, DirectedEdges -> True]
Then
Needs["Combinatorica`"]
and
Neighborhood[nn, 2, 1]
Out[3] = {2, 1 -> 3}
which makes no sense. The answer should be {3,5}.
Even better, try:
Neighborhood[nn, 2, 2]
Out[4]=
Part::pspec: Part specification {2,1->3} is neither an integer nor a
list of integers. >>
Part::pspec: Part specification {2,1->3} is neither an integer nor a
list of integers. >>
Union::heads: Heads Part and List at positions 2 and 1 are expected to
be the same. >>
{2, 1 -> 3} \[Union] {1 -> 2, 1 -> 3, 2 -> 5, 2 -> 3, 3 -> 4, 4 -> 3,
3 -> 6, 5 -> 6}[[{2, 1 -> 3}]]
which is even more entertaining.
regards,
Bernard