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## Re: [igraph] segmenting graphs

 From: Tom Wright Subject: Re: [igraph] segmenting graphs Date: Mon, 05 May 2014 16:42:43 -0400

```Whoops sorry,
t<-graph.empty()
t<-t+vertices(c('r',LETTERS[1:9]))
t['r',LETTERS[1:9],attr='weight']<-c(1,-2,2,-2,2,-6,5,10,-10)
t['A','B']<-1
t['r','A']<-FALSE

I'm trying to implement the Lerchs Grossman algorithm, one step includes
finding the subgraph V{B,A}, detaching it from 'r' and adding it as a
child of 'C'. The new edge C -> B needs to be assigned the summed weight
of the detached subgraph V{B,A}.

Apologies if my terminology is poor, I'm still trying to get this clear
in my head as well as in code.

On Mon, 2014-05-05 at 16:26 -0400, Gábor Csárdi wrote:
> On Mon, May 5, 2014 at 4:18 PM, Tom Wright <address@hidden> wrote:
>         Hi,
>         I'm trying to use iGraph in the R environment and I'm getting
>         confused.
>         It seems to me that what I want to do should be simple but...
>
>         t<-graph.empty()
>         t<-t+vertices(c('r',LETTERS[1:9]))
>         t['r',D.vertices[,1],attr='weight']<-1
>
>
> Error in as.igraph.vs(x, j) : object 'D.vertices' not found
>
>         t['A','B']<-1
>         t['r','A']<-FALSE
>
>         I want to get the subgraph with vertex 'A' as the root, i.e.
>         vertices
>         {'A','B'}
>
>
> What does this really mean? The whole tree rooted at 'A'?
>
>
> graph.neighborhood(t, 'A', order=vcount(t))[[1]]
>
>
> Or something else?
>
>
> Gabor
>
>
> [...]
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