It's because the graph definition in graph tool by default is directed. Declare your graph as myGraph = Graph (directed=False)

On Mon, Jan 7, 2019, 23:49 Christopher Morris < christopher.morris@tu-dortmund.de wrote:

Given an *undirected* graph g with four vertices, I add edges by

g.add_edge_list([(0, 1), (0, 2), (0, 3), (1, 0), (1, 2), (1, 3), (2, 0), (2, 1), (2, 3), (3, 0), (3, 1), (3, 2)]) .

When calling g.num_edges() the result is 12. In my opinion it should be 6, as the graph is undirected? Any ideas?

-- Christopher Morris Algorithm Engineering, Department of Computer Science, TU Dortmund University

https://ls11-www.cs.tu-dortmund.de/staff/morris

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Am 14.12.18 um 11:36 schrieb Christopher Morris:

Given an *undirected* graph g with four vertices, I add edges by

g.add_edge_list([(0, 1), (0, 2), (0, 3), (1, 0), (1, 2), (1, 3), (2, 0), (2, 1), (2, 3), (3, 0), (3, 1), (3, 2)]) .

When calling g.num_edges() the result is 12. In my opinion it should be 6, as the graph is undirected? Any ideas?

Since the graph is undirected, adding (1, 2) and (2, 1) just amounts to adding the same edge _twice_.

In graph-tool, the Graph data structure store multigraphs (directed or not). It's up to the user to ensure that there are no parallel edges.

Best, Tiago