transitive_closure#

transitive_closure(G, reflexive=False)[source]#

Returns transitive closure of a graph

The transitive closure of G = (V,E) is a graph G+ = (V,E+) such that for all v, w in V there is an edge (v, w) in E+ if and only if there is a path from v to w in G.

Handling of paths from v to v has some flexibility within this definition. A reflexive transitive closure creates a self-loop for the path from v to v of length 0. The usual transitive closure creates a self-loop only if a cycle exists (a path from v to v with length > 0). We also allow an option for no self-loops.

Parameters:
GNetworkX Graph

A directed/undirected graph/multigraph.

reflexiveBool or None, optional (default: False)

Determines when cycles create self-loops in the Transitive Closure. If True, trivial cycles (length 0) create self-loops. The result is a reflexive transitive closure of G. If False (the default) non-trivial cycles create self-loops. If None, self-loops are not created.

Returns:
NetworkX graph

The transitive closure of G

Raises:
NetworkXError

If reflexive not in {None, True, False}

References

Examples

The treatment of trivial (i.e. length 0) cycles is controlled by the reflexive parameter.

Trivial (i.e. length 0) cycles do not create self-loops when reflexive=False (the default):

>>> DG = nx.DiGraph([(1, 2), (2, 3)])
>>> TC = nx.transitive_closure(DG, reflexive=False)
>>> TC.edges()
OutEdgeView([(1, 2), (1, 3), (2, 3)])

However, nontrivial (i.e. length greater than 0) cycles create self-loops when reflexive=False (the default):

>>> DG = nx.DiGraph([(1, 2), (2, 3), (3, 1)])
>>> TC = nx.transitive_closure(DG, reflexive=False)
>>> TC.edges()
OutEdgeView([(1, 2), (1, 3), (1, 1), (2, 3), (2, 1), (2, 2), (3, 1), (3, 2), (3, 3)])

Trivial cycles (length 0) create self-loops when reflexive=True:

>>> DG = nx.DiGraph([(1, 2), (2, 3)])
>>> TC = nx.transitive_closure(DG, reflexive=True)
>>> TC.edges()
OutEdgeView([(1, 2), (1, 1), (1, 3), (2, 3), (2, 2), (3, 3)])

And the third option is not to create self-loops at all when reflexive=None:

>>> DG = nx.DiGraph([(1, 2), (2, 3), (3, 1)])
>>> TC = nx.transitive_closure(DG, reflexive=None)
>>> TC.edges()
OutEdgeView([(1, 2), (1, 3), (2, 3), (2, 1), (3, 1), (3, 2)])
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