[igraph] cohesive.blocks()

[MATSUDA, Noriyuki]

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.

----------- Here you go ----------------------------
# Structural Cohesion and Embeddedness: A Hierarchical Concept of  
Social Groups
# James Moody; Douglas R. White
# American Sociological Review, Vol. 68, No. 1. (Feb., 2003), pp.  
103-127.

library(igraph); options(digits=3)

plotting <- function(g,msg){
        V(g)$label=paste("v",1:vcount(g),sep="")
        V(g)$cex=6
        V(g)$color="#FeFeFf"
        plot(g,layout=layout.fruchterman.reingold.grid)
        title(main=msg)
        }
##Main
m <- c(1,2,1,3,1,4,1,5,1,6, 2,3,2,4,2,5,2,7,
        3,4,3,6,3,7, 4,5,4,6,4,7, 5,6,5,7,5,21, 6,7,
        7,8,7,11,7,14,7,19,  8,9,8,11,8,14, 9,10,
        10,12,10,13,11,12,11,14, 12,16,
        13,16, 14,15,15,16,
        17,18,17,19,17,20, 18,20,18,21, 19,20,19,22,19,23,
        20,21, 21,22,21,23, 22,23) - 1
g <- graph(m,directed=F)
plotting(g,msg="Fig.2")

#quartz(width=8,height=8)
gb <- cohesive.blocks(g)
#plot(gb, vertex.size=10, emph=c 
(1,2),layout=layout.fruchterman.reingold)
  # to emphasize blocks 1 & 2 in bgraph

quartz(width=8,height=8)
plotBlocks <- function(g,gblocks,msg){
        V(g)$label=paste("v",1:vcount(g),sep="")
        V(g)$cex=6
	colors <- c 
("#FeFeFf","#FeDeDf","#BeFeBf","#9e9eFf","#Ae8e8f","#7eAe7f")
                V(g)$color[ V(g) %in% gblocks[[2]] ]=colors[2]
                for (k in 1:length(gblocks)){
                        V(g)$color[ V(g) %in% gblocks[[k]] ]=colors[k]
                        }
        plot(g,layout=layout.fruchterman.reingold.grid)
        title(main=msg)
        }
plotBlocks(g,gb$blocks,"Fig.2 by hand")

for (k in 1:length(gb$blocks)){
        b <- gb$blocks[[k]]
        cat("block",k,": cohesion| nodes=", gb$block.cohesion,"| ",b +1,,"\n")
        }
#block 1 : cohesion| nodes= 1 |  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15  
16 17 18 19 20 21 22 23
#block 2 : cohesion| nodes= 2 |  1 2 3 4 5 6 7 17 18 19 20 21 22 23
#block 3 : cohesion| nodes= 2 |  7 8 9 10 11 12 13 14 15 16
#block 4 : cohesion| nodes= 5 |  1 2 3 4 5 6 7
#block 5 : cohesion| nodes= 3 |  7 8 11 14

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MATSUDA, Noriyuki  <Kanji> 松田紀之