#無向グラフを作成する
e.matrix <- matrix(c(1,2,1,3,1,4,2,3),ncol =2 , byrow = TRUE)
e.matrix
     [,1] [,2]
[1,]    1    2
[2,]    1    3
[3,]    1    4
[4,]    2    3
g4 <- graph.edgelist(e.matrix-1, directed = FALSE)
g4
Vertices: 4 
Edges: 4 
Directed: FALSE 
Edges:
          
[0] 0 -- 1
[1] 0 -- 2
[2] 0 -- 3
[3] 1 -- 2
png("110214.g4.png")
plot(g4)
dev.off()
