[igraph] Puzzling error message

[David Edwards]

Dear help list

 

I would like to display directed graphs so that reciprocal edges are plotted without arrows. The following code

 

em1 <- c(0,0,1,1,1,0,1,1,1,1,0,1,1,1,1,0); dim(em1)<- c(4,4)
iG <- graph.adjacency(em1)  
E(iG)$arrow.mode <- 2
E(iG)[is.mutual(iG)]$arrow.mode <- 0
iG$layout <- layout.graphopt
plot(iG)

 

works fine but when I change the graph slightly using instead

 

em1 <- c(0,1,1,1,1,0,1,1,1,1,0,1,1,1,1,0); dim(em1)<- c(4,4)

 

(which is symmetric, so all edges are reciprocal), plot gives the message

 

Warning messages:
1: In if (code %in% c(2, 3)) { :
  the condition has length > 1 and only the first element will be used
2: In if (code %in% c(1, 3)) { :
  the condition has length > 1 and only the first element will be used

which I don't understand. What am I doing wrong?

 

Kind regards

David Edwards Senior scientist

Dept. of Genetics and Biotechnology Faculty of Agricultural Sciences Aarhus University Blichers Allé 20, Postboks 50 DK-8830 Tjele

Tel.: +45 8999 1297 Email: address@hidden

Tel.: +45 8999 1900 Web: www.agrsci.au.dk