I'm using the R interface, but I also looked at the C interface. If I got it right, in the C interface vertex indices start from 0, while in R they start from 1 (that's good and natural for R).
However, the get.isomorphism functions return zeros in the mappings, e.g.
> g1=graph.edgelist(cbind(c(1,2,3,4),c(2,3,4,1)))
> g2=graph.edgelist(cbind(c(2,4,1,3),c(4,1,3,2)))
> graph.get.isomorphisms.vf2(g1,g2)
[[1]]
[1] 0 2 1 3
[[2]]
[1] 1 3 2 0
[[3]]
[1] 2 0 3 1
[[4]]
[1] 3 1 0 2
This seems inconsistent with the 1-based indexing of R.
Also, some other functions return maps which don't use 0:
> graph.isomorphic.vf2(g1,g2)
$iso
[1] TRUE
$map12
[1] 1 3 2 4
$map21
[1] 1 3 2 4
Is this by design, or is it an oversight?
Szabolcs