Warning

This documents an unmaintained version of NetworkX. Please upgrade to a maintained version and see the current NetworkX documentation.

# Source code for networkx.algorithms.components.semiconnected

# -*- coding: utf-8 -*-
#    Aric Hagberg <hagberg@lanl.gov>
#    Dan Schult <dschult@colgate.edu>
#    Pieter Swart <swart@lanl.gov>
#
"""Semiconnectedness."""
import networkx as nx
from networkx.utils import not_implemented_for, pairwise

__all__ = ['is_semiconnected']

[docs]@not_implemented_for('undirected')
def is_semiconnected(G):
"""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.

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

--------
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))