65 lines
1.6 KiB
Python
65 lines
1.6 KiB
Python
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"""Semiconnectedness."""
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import networkx as nx
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from networkx.utils import not_implemented_for, pairwise
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__all__ = ["is_semiconnected"]
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@not_implemented_for("undirected")
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def is_semiconnected(G, topo_order=None):
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"""Returns True if the graph is semiconnected, False otherwise.
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A graph is semiconnected if, and only if, for any pair of nodes, either one
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is reachable from the other, or they are mutually reachable.
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Parameters
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----------
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G : NetworkX graph
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A directed graph.
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topo_order: list or tuple, optional
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A topological order for G (if None, the function will compute one)
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Returns
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-------
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semiconnected : bool
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True if the graph is semiconnected, False otherwise.
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Raises
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------
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NetworkXNotImplemented
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If the input graph is undirected.
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NetworkXPointlessConcept
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If the graph is empty.
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Examples
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--------
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>>> G = nx.path_graph(4, create_using=nx.DiGraph())
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>>> print(nx.is_semiconnected(G))
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True
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>>> G = nx.DiGraph([(1, 2), (3, 2)])
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>>> print(nx.is_semiconnected(G))
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False
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See Also
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--------
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is_strongly_connected
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is_weakly_connected
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is_connected
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is_biconnected
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"""
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if len(G) == 0:
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raise nx.NetworkXPointlessConcept(
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"Connectivity is undefined for the null graph."
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)
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if not nx.is_weakly_connected(G):
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return False
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G = nx.condensation(G)
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if topo_order is None:
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topo_order = nx.topological_sort(G)
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return all(G.has_edge(u, v) for u, v in pairwise(topo_order))
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