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[igraph] Graph isomorphism missed?

From: Louis Aslett
Subject: [igraph] Graph isomorphism missed?
Date: Wed, 12 Sep 2012 14:22:17 +0100

I might have misunderstood coloured graph isomorphisms, but from my
understanding the following two graphs should be isomorphic (code in

g1 <- graph.formula(1 -- 2:3, 2 -- 3, 3 -- 4)
g2 <- graph.formula(1 -- 2, 2 -- 3, 2:3 -- 4)
graph.count.isomorphisms.vf2(g1, g2, vertex.color1=c(1,2,2,1),

My understanding of coloured isomorphism is that two bijections are
looked for f and g, say, such that f applied to one colour or vertex
and g to the other results in equivalent adjacency to the original
graph.  In this case, bijection f which switches 1 and 4, and another
g which switches 2 and 3 does the job (I think).  However, the
function says there are no isomorphisms.

Any thoughts (or corrections to my understanding of coloured
isomorphism) appreciated!


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