# triads.py - generators for triad graphs
#
# Copyright 2015 NetworkX developers.
# Copyright 2011 Reya Group <http://www.reyagroup.com>
# Copyright 2011 Alex Levenson <alex@isnotinvain.com>
# Copyright 2011 Diederik van Liere <diederik.vanliere@rotman.utoronto.ca>
#
# This file is part of NetworkX.
#
# NetworkX is distributed under a BSD license; see LICENSE.txt for more
# information.
"""Functions that generate the triad graphs, that is, the possible
digraphs on three nodes.
"""
from networkx.classes import DiGraph
__all__ = ['triad_graph']
#: Dictionary mapping triad name to list of directed edges in the
#: digraph representation of that triad (with nodes 'a', 'b', and 'c').
TRIAD_EDGES = {'003': [],
'012': ['ab'],
'102': ['ab', 'ba'],
'021D': ['ba', 'bc'],
'021U': ['ab', 'cb'],
'021C': ['ab', 'bc'],
'111D': ['ac', 'ca', 'bc'],
'111U': ['ac', 'ca', 'cb'],
'030T': ['ab', 'cb', 'ac'],
'030C': ['ba', 'cb', 'ac'],
'201': ['ab', 'ba', 'ac', 'ca'],
'120D': ['bc', 'ba', 'ac', 'ca'],
'120U': ['ab', 'cb', 'ac', 'ca'],
'120C': ['ab', 'bc', 'ac', 'ca'],
'210': ['ab', 'bc', 'cb', 'ac', 'ca'],
'300': ['ab', 'ba', 'bc', 'cb', 'ac', 'ca']
}
[docs]def triad_graph(triad_name):
"""Returns the triad graph with the given name.
Each string in the following tuple is a valid triad name::
('003', '012', '102', '021D', '021U', '021C', '111D', '111U',
'030T', '030C', '201', '120D', '120U', '120C', '210', '300')
Each triad name corresponds to one of the possible valid digraph on
three nodes.
Parameters
----------
triad_name : string
The name of a triad, as described above.
Returns
-------
:class:`~networkx.DiGraph`
The digraph on three nodes with the given name. The nodes of the
graph are the single-character strings 'a', 'b', and 'c'.
Raises
------
:exc:`ValueError`
If `triad_name` is not the name of a triad.
See also
--------
triadic_census
"""
if triad_name not in TRIAD_EDGES:
raise ValueError('unknown triad name "{}"; use one of the triad names'
' in the TRIAD_NAMES constant'.format(triad_name))
G = DiGraph()
G.add_nodes_from('abc')
G.add_edges_from(TRIAD_EDGES[triad_name])
return G