Re: [igraph] shortest path calculation

[Gábor Csárdi]

On Fri, Jan 30, 2009 at 5:45 PM, Thiago M. Venancio
<address@hidden> wrote:
> Thanks Gabor !
> It worked.
> My toy file is simple:
>
> #=======
> a b
> b c
> c d
> #=======

Sorry, but that is still not good enough, there might be spaces after
the edges and the 'ncol' reader might interpret these as weights
(which would be a bug). Anyway, I will check this, but it is a lot
easier if you provide ALL information to reproduce the error.

> The interesting point is that the shortest.paths function does not work
> without assigning the weights=FALSE, but the average.path.length and
> path.length.hist work without any problems. Since they are related, I was
> just wondering what is different in how they handle the data.

The latter two don't support edge weights.

G.

> Best,
>
> Thiago
>
> On Fri, Jan 30, 2009 at 11:40 AM, Gábor Csárdi <address@hidden> wrote:
>>
>> Hmmm, again I cannot be sure what happens, because I haven't seen your
>> file. Anyway, giving 'weights=FALSE' to read.graph should solve the
>> problem.
>>
>> G.
>>
>> On Fri, Jan 30, 2009 at 5:37 PM, Thiago M. Venancio
>> <address@hidden> wrote:
>> > Hi Gabor,
>> > You got it right. There is no weight in the file. Assigning one does the
>> > trick.
>> > My graph is unweighted, is there any way to assign 1 during the file
>> > reading
>> > or do I have to change the file to include an useless column with ones ?
>> > Thank you very much.
>> > Thiago
>> >
>> > On Fri, Jan 30, 2009 at 11:33 AM, Gábor Csárdi <address@hidden>
>> > wrote:
>> >>
>> >> Impossible to tell for sure without knowing what is in the file "b".
>> >> My guess is that all edges have weight zero, but can be something
>> >> else.
>> >>
>> >> G.
>> >>
>> >> On Fri, Jan 30, 2009 at 5:30 PM, Thiago M. Venancio
>> >> <address@hidden> wrote:
>> >> > Hi,
>> >> >
>> >> > I am experiencing some problems in calculating the shortest path
>> >> > length
>> >> > matrix. Note that it is giving zeroes for all the cells, even when
>> >> > vertices
>> >> > are connected.
>> >> > I noticed the V() function return indexes in the indexes and in my
>> >> > graph
>> >> > return quoted numbers. Explicitly telling the indexes also does not
>> >> > solve
>> >> > the problem.
>> >> > The example in the documentation is working. I do not know what is
>> >> > the
>> >> > problem in my code.
>> >> > Below is a toy example.
>> >> >
>> >> > Thanks.
>> >> >
>> >> > Thiago
>> >> >
>> >> > test = read.graph("b", format="ncol", names=T)
>> >> >> test
>> >> > Vertices: 4
>> >> > Edges: 3
>> >> > Directed: FALSE
>> >> > Edges:
>> >> >
>> >> > [0] a -- b
>> >> > [1] b -- c
>> >> > [2] c -- d
>> >> >
>> >> >> shortest.paths(test)
>> >> >      [,1] [,2] [,3] [,4]
>> >> > [1,]    0    0    0    0
>> >> > [2,]    0    0    0    0
>> >> > [3,]    0    0    0    0
>> >> > [4,]    0    0    0    0
>> >> >
>> >> >> shortest.paths(test,v=1:2)
>> >> >      [,1] [,2] [,3] [,4]
>> >> > [1,]    0    0    0    0
>> >> > [2,]    0    0    0    0
>> >> >
>> >> >
>> >> >
>> >> > _______________________________________________
>> >> > igraph-help mailing list
>> >> > address@hidden
>> >> > http://lists.nongnu.org/mailman/listinfo/igraph-help
>> >> >
>> >> >
>> >>
>> >>
>> >>
>> >> --
>> >> Gabor Csardi <address@hidden>     UNIL DGM
>> >>
>> >>
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>> >
>> >
>> >
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>> >
>>
>>
>>
>> --
>> Gabor Csardi <address@hidden>     UNIL DGM
>>
>>
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-- 
Gabor Csardi <address@hidden>     UNIL DGM