#18067: sage/graphs/graph.py: multigraph recognition in init fails
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Reporter: darij | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.6
Component: graph theory | Keywords: graphs, sage-combinat,
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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The idea seems to be that the `__init__` method of `Graph` should check if
the user provides some edges more than 1 time, and, if so, return a
multigraph instead of a graph. In reality, whether this happens depends on
the order of vertices the user provides:
{{{
sage: Graph([[1,2],[1,2]])
Multi-graph on 2 vertices
sage: Graph([[1,2],[2,1]])
Graph on 2 vertices
}}}
Apparently, it is the `if len(set(data[u])) != len(data[u])` conditional
on line 1497 of graph.py which fails to fire in the second example.
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Ticket URL: <http://trac.sagemath.org/ticket/18067>
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