[igraph] unexpected behaviour graph.count.subisomorphisms.vf2

[Christopher Knight]

Hi, 

I'm trying to use graph.count.subisomorphisms.vf2() and graph.get.subisomorphisms.vf2() in R on graphs with coloured edges. However, this doesn't behave as I expect.  This could be a bug, or it's possible I've misunderstood something fundamental about what these functions are meant to do. Specifically:

#create a directed ring graph with alternating edge colours

library(igraph)

g1 <- graph.ring(10,directed=TRUE)

E(g1)$color <- rep(1:2, length=ecount(g1))

#create a simple A-->B-->C graph with two edge colours

g2<-graph.edgelist(el=matrix(c(1,2,2,3),nrow=2,byrow=TRUE),directed=TRUE)

E(g2)$color<-c(1,2)

#count isomorphisms ignoring colours

graph.count.subisomorphisms.vf2(g1, g2, edge.color1=NULL, edge.color2=NULL)

#10 as expected

#count isomorphisms using colours

graph.count.subisomorphisms.vf2(g1, g2)

#6 - I expected 5 (one for each occurrence of a colour in g1) and what these are when looked at with graph.get.subisomorphisms.vf2(g1, g2) seems inexplicable to me.

#change colours for subgraph edges to the same value, a sequence which doesn't occur in g1 at all, and count isomorphisms again

E(g2)$color<-c(1,1)

graph.count.subisomorphisms.vf2(g1, g2)

#expect a change to zero, but get 6 again

Any help much appreciated.

thanks,

Chris

sessionInfo()

R version 2.15.1 (2012-06-22)

Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:

[1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8

attached base packages:

[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:

[1] igraph_0.6-2

------------------------------------------------------------------------
Dr Christopher Knight                             Michael Smith Building
Wellcome Trust RCD Fellow                       Faculty of Life Sciences
Tel:  +44 (0)161 2755378                    The University of Manchester
room B.2012                                                  Oxford Road
tinyurl.com/knightLab/                                Manchester M13 9PT
· . ,,><(((°>                                                         UK
------------------------------------------------------------------------