Groups > comp.soft-sys.math.mathematica > #2298

Re: Strange result with FindShortestPath and Tuple

From	Oliver Ruebenkoenig <ruebenko@wolfram.com>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Re: Strange result with FindShortestPath and Tuple
Date	2011-05-12 08:33 +0000
Organization	Steven M. Christensen and Associates, Inc and MathTensor, Inc.
Message-ID	<iqg5vs$d2p$1@smc.vnet.net> (permalink)

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On Wed, 11 May 2011, Szabolcs Horv=E1t wrote:

> On 2011.05.10. 14:32, Julian Francis wrote:
>> 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

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Re: Strange result with FindShortestPath and Tuple Oliver Ruebenkoenig <ruebenko@wolfram.com> - 2011-05-12 08:33 +0000
  Re: Strange result with FindShortestPath and Tuple Julian Francis <julian.w.francis@gmail.com> - 2011-05-31 11:54 +0000

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