Re: [igraph] connected graph returns shortest.paths with inf

[Martin Tomko]

Thanks Tamas, will do some more testing here and will email you if the 
problem persists. I have tried testing with a different graph now (which 
is definitely connected), and it seems to work.
The problem I had was after reading in a disconnected graph and running 
(in igraph 0.5.2-2, R 2.9.2, Win XP):

if(is.connected(g)==FALSE){
        c <- clusters(g)
        g <- subgraph(g,which(c$membership==which.max(c$csize)-1)-1);
    }

Anyway, will test more and get back to you.
Martin

On 9/1/2010 11:14 AM, Tamas Nepusz wrote:
> Dear Martin,
>
>    
> > nodes<- V(g);
> > y<-lapply(nodes,function(x){shortest.paths(g,x)})
> >
> > max(y[[1]]) returns Inf, and also sum(y[[1]]==Inf), meaning that
> > there are disconnected nodes.
> >
> > How could that happen?
> >      
> First I was thinking that is.connected() in R may be checking for strong
> connectedness and your graph may be only weakly connected (meaning that
> there is a path from A to B but no path from B to A); however, it turns
> out not to be the case (at least not in 0.6). I'm not that familiar with
> the R interface, but if you can send me a small(ish) example graph on
> which I could reproduce the problem, I'll take a look.
>
> Cheers,
> Tamas
>
>
>    


--
Martin Tomko
Postdoctoral Research Assistant

Geographic Information Systems Division
Department of Geography
University of Zurich - Irchel
Winterthurerstr. 190
CH-8057 Zurich, Switzerland

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