Re: [igraph] issue with giant component in python-igraph

[Tamas Nepusz]

Dear Anirban,

> G = igraph.load(sys.argv[1], format="edgelist", directed=True)
> components = G.clusters(igraph.WEAK)
> igraph.save(components.subgraph(0), "giantcomponent.txt",  
> format="edgelist")
That looks OK, the only thing I'd done differently is that  
VertexClustering objects (like what you got in components) have a  
method called .giant(), so you don't have to check the component sizes  
manually. So theoretically it's OK what you are doing. You might try  
the following to find out where the bug is:

- instead of G.clusters(igraph.WEAK), try igraph.GraphBase.clusters(G,  
igraph.WEAK) which calls the underlying C implementation directly and  
results a single list l where l[i] equals the index of the cluster  
where the ith vertex belongs to. There might be a bug in the creation  
of a VertexClustering object.

- try to go even deeper and write the above program in C -- it boils  
down to calling igraph_read_graph_edgelist, igraph_clusters and  
igraph_write_graph_edgelist in the right order ;)

- if your graph is not confidential, you can try to upload it  
somewhere and send me the URL where I can download it form. I will try  
to reproduce your bug in my own machine. (Otherwise, if you manage to  
construct a similar graph that also reproduces the problem, that's  
fine).

--
Tamas