Re: [igraph] One-mode projection: Problem understanding increase of number of edges

[Gábor Csárdi]

Hi, here is a simple example that helps understand it:

g <- graph.star(100, mode="undirected", center=1)
V(g)$type <- c(FALSE, rep(TRUE, 99))
bipartite.projection(g)

# $proj1
# IGRAPH U--B 1 0 -- Star
# + attr: name (g/c), mode (g/c), center (g/n), type (v/x)
#
# $proj2
# IGRAPH U-WB 99 4851 -- Star
# + attr: name (g/c), mode (g/c), center (g/n), type (v/x), weight (e/n)

Gabor

On Fri, Nov 15, 2013 at 5:50 PM,  <address@hidden> wrote:
> Hello,
>
> I have been scratching my head in trying to understand the result of a
> one-mode projection of a bipartite graph.
>
> This is the bipartite graph
>
>     > graph_bi
>     IGRAPH DN-B 154625 448384 --
>
> and after bipartite.projection(graph_bi) these are the two projections
>
>     > graph_onemode$proj1
>     IGRAPH UNWB 79186 13259012 --
>
>
>     > graph_onemode$proj2
>     IGRAPH UNWB 75439 50375826 --
>
>
> Now, my intuition doesn't help here. Simply, How is possible that the number
> of edges in the two projections increases by 29 and 112 times respectively?
>
> I am probably missing something here but as I understand the one-mode
> projection the number of edges should actually decrease. A-B and B-C (where
> A and C are type 1 nodes and B is a type 2 node) should be projected to A-C
> thus halving the number of edges...
>
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