[igraph] vf2 isormorphism multi-graph

[Steven Harenberg]

Hi,

I am running VF2 in igraph (with python interface) and it seems that the
algorithm in igraph does not properly support isomorphism with multiple
edges between the same two vertices.

Example:

import igraph

Q = igraph.Graph(directed=True)
Q.add_vertices(2)
Q.add_edges([(0,1)])

G = igraph.Graph(directed=True)
G.add_vertices(2)
G.add_edges([(0,1), (0,1)])

print G.get_subisomorphisms_vf2(Q, edge_color1=[1,2], edge_color2=[1]) #
empty
print G.get_subisomorphisms_vf2(Q, edge_color1=[2,1], edge_color2=[1]) #
one mapping

Is this a known issue? I have seen a few comments around suggesting to use
the multiplicity of edges as labels to include in the match, but based on
the above example, this still seems problematic unless I am misinterpreting
something. Are there any ongoing plans for vf2 to support multiple edges
between the same two nodes?

Thanks,
Steve