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