def underlying_graph(G):
r"""
Given a graph `G` with multi-edges, returns a graph where all the
multi-edges are replaced with a single edge.
EXAMPLES::
sage: from sage.graphs.tutte_polynomial import underlying_graph
sage: G = Graph(multiedges=True)
sage: G.add_edges([(0,1,'a'),(0,1,'b')])
sage: G.edges()
[(0, 1, 'a'), (0, 1, 'b')]
sage: underlying_graph(G).edges()
[(0, 1, None)]
"""
g = Graph()
g.allow_loops(True)
for edge in set(G.edges(labels=False)):
g.add_edge(edge)
return g
def underlying_graph(G):
r"""
Given a graph `G` with multi-edges, returns a graph where all the
multi-edges are replaced with a single edge.
EXAMPLES::
sage: from sage.graphs.tutte_polynomial import underlying_graph
sage: G = Graph(multiedges=True)
sage: G.add_edges([(0,1,'a'),(0,1,'b')])
sage: G.edges()
[(0, 1, 'a'), (0, 1, 'b')]
sage: underlying_graph(G).edges()
[(0, 1, None)]
"""
g = Graph()
g.allow_loops(True)
for edge in set(G.edges(labels=False)):
g.add_edge(edge)
return g
