Re: Strange result with FindShortestPath and Tuple
- To: mathgroup at smc.vnet.net
- Subject: [mg119357] Re: Strange result with FindShortestPath and Tuple
- From: Julian Francis <julian.w.francis at gmail.com>
- Date: Tue, 31 May 2011 07:53:51 -0400 (EDT)
- References: <iqg5vs$d2p$1@smc.vnet.net>
Dear Oliver & Szabolcs,
Thanks for both of your replies. Let's hope it gets fixed in the next
Mathematica release.
Thanks & kind regards,
Julian.
On May 12, 9:33 am, Oliver Ruebenkoenig <ruebe... at wolfram.com> wrote:
> On Wed, 11 May 2011, Szabolcs Horv=E1t wrote:
> > On 2011.05.10. 14:32, JulianFranciswrote:
> >> Dear all,
>
> >> I am getting a very confusing result when using Tuple to build a list
> >> of vertices to be used as input to Graph (and eventually
> >> FindShortestPath). However, when I use Table to build the list of
> >> vertices, it all works fine. But the output of Tuple and Table produce
> >> identical expressions, so why would one work and not the other? A
> >> simple example may illustrate what I mean more clearly:
>
> >> In[1]:= vertices1 = Tuples[{Range[2], Range[2]}]
>
> >> Out[1]= {{1, 1}, {1, 2}, {2, 1}, {2, 2}}
>
> >> In[2]:= vertices2 = Flatten[Table[{x, y}, {x, 1, 2}, {y, 1, 2}], 1=
]
>
> >> Out[2]= {{1, 1}, {1, 2}, {2, 1}, {2, 2}}
>
> >> In[3]:= vertices1 === vertices2
>
> >> Out[3]= True
>
> >> In[8]:= FindShortestPath[
> >> Graph[vertices1, {{1, 1} \[DirectedEdge] {2, 1}},
> >> VertexLabels -> "Name"], {1, 1}, {2, 1}]
>
> >> Out[8]= {1, 1}
>
> >> In[9]:= FindShortestPath[
> >> Graph[vertices2, {{1, 1} \[DirectedEdge] {2, 1}},
> >> VertexLabels -> "Name"], {1, 1}, {2, 1}]
>
> >> Out[9]= {{1, 1}, {2, 1}}
>
> >> I was expecting the last two expressions to be the same (with the last
> >> one being the correct one). Why the difference?
>
> >> Any help would be greatly appreciated.
>
> > I believe this is a bug.
>
> > I'm replying just to mention that the difference between vertices1 and
> > vertices2 is that vertices1 is a packed array:
>
> > Developer`PackedArrayQ[vertices1]
>
> > gives True.
>
> I reported it as bug. Thanks.
>
> Oliver