[igraph] Constraints Preventing large

[Ulrike Grömping]

Dear igraph helpers,

I am searching for subgraphs within a structured graph. Both the graph itself
and the potential subgraph have nfac "outer" vertices and nfac(nfac-1)/2
"inner" vertices. They differ only in the edges between inner vertices. Outer
vertices must remain outer vertices, so that colored matching in VF2 would
make this task possible (but slow). 

However, I have just realized that the ideal way to treat my graph would be to
keep the inner vertices in position and only permute the outer vertices. This
would of course greatly reduce the number of permitted permutations. Is there
any way to incorporate such constraints in the isomorphism check? I think I've
seen a similar question asked before, and answered in terms of colors, but
it's not the same, is it ? So far, I have come up with the workaround (not yet
implemented) to manually permute vertices and check the subgraph property by
checking the difference of the subgraph candidate (as big) to the larger graph
for having 0 edges (-->subgraph).

Regards, Ulrike