Re: [igraph] subtraction?

[Tamas Nepusz]

Hi Marco,

It depends on how that subgraph is specified. If you know the assignment
between vertices of g and h (i.e., you know that, say, vertex X in h
belongs to vertex Y in g for all X), you can simply use igraph_subgraph()
in C or Graph.subgraph() in Python (sorry, I don't know it by heart for R,
but I guess it's simply subgraph()), or you can also use
igraph_delete_vertices() or Graph.delete_vertices() on g if you don't
need g afterwards.

If you don't know the mapping from vertices of h to vertices of g, but
you know that h is a subgraph of g and it is unique, you can use
igraph_get_subisomorphisms_vf2 (or Graph.get_subisomorphisms_vf2) to
find the mapping from vertices of h to vertices of g.

-- 
Tamas

On Thu, May 21, 2009 at 11:44:19AM +0200, Marco wrote:
> Hi all list!
> 
> Let's suppose I have a graph g, and a subgraph of g, let's call it h.
> I'd like to build the graph that is defined of all the vertices in g
> that are not in h.
> Edges are kept the same as in g if both the endvertices survive, or
> are deleted if at least one of the endvertices is killed.
> 
> How do it efficiently in igraph?
> 
> thanks in advance as always,
> 
> marco
> 
> --
> restituiremo il riso ai salici
> 
> 
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