# -*- coding: utf-8 -*-
# Copyright (C) 2004-2016 by
# Aric Hagberg <hagberg@lanl.gov>
# Dan Schult <dschult@colgate.edu>
# Pieter Swart <swart@lanl.gov>
# All rights reserved.
# BSD license.
#
# Authors: ysitu (ysitu@users.noreply.github.com)
"""Semiconnectedness."""
import networkx as nx
from networkx.utils import not_implemented_for, pairwise
__all__ = ['is_semiconnected']
@not_implemented_for('undirected')
[docs]def is_semiconnected(G):
"""Return 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.
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)
path = nx.topological_sort(G)
return all(G.has_edge(u, v) for u, v in pairwise(path))