[igraph] Network with directed and undirected edges

[Dieckmann, Anna]

Dear all, 

I've to build a protein-protein-interaction network with mainly undirected but 
also some directed edges. Is there any way to build such a network with igraph? 
As I'll have to analyze e.g. the topology and to calculate the different 
centrality measures, I'd very much like to stick to using igraph for my Phd 
project :)

Many thanks in advance, 
Anna