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From: | Gábor Csárdi |
Subject: | Re: [igraph] biconnected.components vs cohesive.blocks |
Date: | Thu, 4 Jul 2013 10:25:03 -0400 |
[Using igraph ‘0.6.5.1’ under R]
I noticed that cohesive blocks (with cohesion equal to 2) and biconnected components of a graph might differ (to my knowledge, they should be the same). Here's an example:
# Load Newman's network science collaboration graph
# (http://www-personal.umich.edu/~mejn/netdata/netscience.zip)
g = read.graph(file="netscience.gml", format="gml")
# Get the giant component of the graph
cl = clusters(g)
g = induced.subgraph(g, which(cl$membership == which.max(cl$csize)))
# Get cohesive blocks
cb = cohesive.blocks(g)
b = blocks(cb)
# Get the largest cohesive block with cohesion 2 (number 69, should be the largest biconnected component)
g1 = induced.subgraph(g, b[[69]])
# Get biconnected components
bc = biconnected.components(g)
c = bc$components
# Get the largest biconnected component (number 86)
g2 = induced.subgraph(g, c[[86]])
> graph.cohesion(g1)
[1] 2
> graph.cohesion(g2)
[1] 2
Now, g1 and g2 should be the same graph, but:
> g1
IGRAPH U--- 56 171 --
+ attr: id (v/n), label (v/c), value (e/n)
> g2
IGRAPH U--- 134 372 --
+ attr: id (v/n), label (v/c), value (e/n)
Thanks,
Massimo Franceschet
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