Hi,
I encountered a strange behaviour of the add_edges method for DiGraphs
(using SAGE 4.5.1). Perhaps this is intended behaviour, but as it
seems quiet odd to me I would like to hear the opinion of more
experienced (di)graph-users. Maybe this is a real bug...
If I define a looped, multi-edge empty digraph with
G=DiGraph({},multi_edges=True,loops=True)
I can add a couple of edges at once using
G.add_edges([[0,1],[0,1],[1,1],[0,0],[1,0],[0,1]])
this gives the correct graph (having 2 vertices and 6 edges).
Nevertheless, if I define my digraph with
G=DiGraph(multi_edges=True,loops=True)
or
G=DiGraph([],multi_edges=True,loops=True)
the same command to add edges
G.add_edges([[0,1],[0,1],[1,1],[0,0],[1,0],[0,1]])
gives a digraph on 2 vertices but with only 4 edges (the double edge
is not created).
Even stranger: If I put edge labels I can see that whenever I add more
edges afterwards an old edge gets deleted and is replaced by a new
one, but never does the graph have multi-edges.
Looking forward to an explanation of this funny behaviour.
Best
M.
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