Re: [igraph] cohesive.blocks()

[MATSUDA, Noriyuki]

Hello:

   I know cohesive.blocks() extracts two blocks that are cliques.
      block4:   {1-7}
      block 5:  {7,8,11,14)

But, I have an impression, from the explanations about Figures 2
and 3 in Moody and White's paper, another one is embedded in
the figures:
        {17,18,19,20,21,22,23}  (not a clique)
   This is derivable from the output of cohesive.blocks().  Yet I'd
be happy if the group were directly obtainable, if it is cohesive (
to a lesser extent than a clique).

    I know that  a set {8, 9, 10, 11, 12, 14, 15} is not cohesive.

Thanks.
On 2008/04/28, at 23:30, Gabor Csardi wrote:

> Hello,
>
> to be honest, i don't really understand the question.
> In your graph (==block 1, cohesion 1) the algorithm finds
> two sub-blocks (block 2, cohesion 2, and block 3, cohesion 2).
> In block 2 there is a (more) cohesive sub-block, this
> will be block 4, it has cohesion 5. Within block 3, there is
> a 3-cohesive block, this will be block 5.
>
> In the last case, the remainder of block 3, i.e. the vertices
> not in block 5 (vertices 8, 9, 10, 11, 12, 14, 15) do not
> constitute a cohesive block, that's why they are not included in
> the result.
>
> If in a B cohesive block there is a sub-block C with higher
> cohesion value, that does not mean that B-C (the remainder)
> has a higher cohesion value (than the original B block) as well.
>
> Does this answer your question?
> Gabor.
>
> On Mon, Apr 28, 2008 at 05:54:20PM +0900, MATSUDA, Noriyuki wrote:
> > Hello:
> >
> >    I have some difficulty in relating the performance of
> > cohesive.blocks() to the original paper by Moody and White (2003),
> > particularly the concepts of components and blocks.  Here is my trial
> > on Figures 2 and 3 in the paper:
> >   It separates terminal (bottom) blocks 4 and 5, leaving  {17-23}
> > unextracted.   Do we need to identify {17-23} by taking the
> > difference between blocks 2 and 4?  If so, it would require a lot of
> > care even with a graph of medium size.  Or have I made errors in
> > specifying edges?
> >   Thanks in advance for helping me out.
> [...]
>
> --
> Csardi Gabor <address@hidden>    UNIL DGM
>
>
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MATSUDA, Noriyuki  <Kanji> 松田紀之