554 lines
18 KiB
Python
554 lines
18 KiB
Python
# Copyright (C) 2004-2019 by
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# Aric Hagberg <hagberg@lanl.gov>
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# Dan Schult <dschult@colgate.edu>
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# Pieter Swart <swart@lanl.gov>
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# All rights reserved.
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# BSD license.
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"""Functions for finding and manipulating cliques.
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Finding the largest clique in a graph is NP-complete problem, so most of
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these algorithms have an exponential running time; for more information,
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see the Wikipedia article on the clique problem [1]_.
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.. [1] clique problem:: https://en.wikipedia.org/wiki/Clique_problem
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"""
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from collections import deque
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from itertools import chain
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from itertools import combinations
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from itertools import islice
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try:
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from itertools import ifilter as filter
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except ImportError:
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pass
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import networkx as nx
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from networkx.utils import not_implemented_for
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__author__ = """Dan Schult (dschult@colgate.edu)"""
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__all__ = ['find_cliques', 'find_cliques_recursive', 'make_max_clique_graph',
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'make_clique_bipartite', 'graph_clique_number',
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'graph_number_of_cliques', 'node_clique_number',
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'number_of_cliques', 'cliques_containing_node',
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'enumerate_all_cliques']
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@not_implemented_for('directed')
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def enumerate_all_cliques(G):
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"""Returns all cliques in an undirected graph.
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This function returns an iterator over cliques, each of which is a
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list of nodes. The iteration is ordered by cardinality of the
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cliques: first all cliques of size one, then all cliques of size
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two, etc.
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Parameters
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----------
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G : NetworkX graph
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An undirected graph.
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Returns
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-------
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iterator
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An iterator over cliques, each of which is a list of nodes in
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`G`. The cliques are ordered according to size.
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Notes
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-----
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To obtain a list of all cliques, use
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`list(enumerate_all_cliques(G))`. However, be aware that in the
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worst-case, the length of this list can be exponential in the number
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of nodes in the graph (for example, when the graph is the complete
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graph). This function avoids storing all cliques in memory by only
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keeping current candidate node lists in memory during its search.
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The implementation is adapted from the algorithm by Zhang, et
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al. (2005) [1]_ to output all cliques discovered.
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This algorithm ignores self-loops and parallel edges, since cliques
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are not conventionally defined with such edges.
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References
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----------
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.. [1] Yun Zhang, Abu-Khzam, F.N., Baldwin, N.E., Chesler, E.J.,
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Langston, M.A., Samatova, N.F.,
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"Genome-Scale Computational Approaches to Memory-Intensive
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Applications in Systems Biology".
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*Supercomputing*, 2005. Proceedings of the ACM/IEEE SC 2005
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Conference, pp. 12, 12--18 Nov. 2005.
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<https://doi.org/10.1109/SC.2005.29>.
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"""
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index = {}
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nbrs = {}
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for u in G:
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index[u] = len(index)
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# Neighbors of u that appear after u in the iteration order of G.
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nbrs[u] = {v for v in G[u] if v not in index}
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queue = deque(([u], sorted(nbrs[u], key=index.__getitem__)) for u in G)
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# Loop invariants:
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# 1. len(base) is nondecreasing.
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# 2. (base + cnbrs) is sorted with respect to the iteration order of G.
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# 3. cnbrs is a set of common neighbors of nodes in base.
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while queue:
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base, cnbrs = map(list, queue.popleft())
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yield base
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for i, u in enumerate(cnbrs):
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# Use generators to reduce memory consumption.
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queue.append((chain(base, [u]),
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filter(nbrs[u].__contains__,
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islice(cnbrs, i + 1, None))))
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@not_implemented_for('directed')
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def find_cliques(G):
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"""Returns all maximal cliques in an undirected graph.
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For each node *v*, a *maximal clique for v* is a largest complete
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subgraph containing *v*. The largest maximal clique is sometimes
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called the *maximum clique*.
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This function returns an iterator over cliques, each of which is a
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list of nodes. It is an iterative implementation, so should not
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suffer from recursion depth issues.
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Parameters
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----------
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G : NetworkX graph
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An undirected graph.
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Returns
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-------
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iterator
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An iterator over maximal cliques, each of which is a list of
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nodes in `G`. The order of cliques is arbitrary.
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See Also
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--------
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find_cliques_recursive
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A recursive version of the same algorithm.
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Notes
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-----
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To obtain a list of all maximal cliques, use
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`list(find_cliques(G))`. However, be aware that in the worst-case,
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the length of this list can be exponential in the number of nodes in
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the graph. This function avoids storing all cliques in memory by
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only keeping current candidate node lists in memory during its search.
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This implementation is based on the algorithm published by Bron and
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Kerbosch (1973) [1]_, as adapted by Tomita, Tanaka and Takahashi
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(2006) [2]_ and discussed in Cazals and Karande (2008) [3]_. It
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essentially unrolls the recursion used in the references to avoid
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issues of recursion stack depth (for a recursive implementation, see
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:func:`find_cliques_recursive`).
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This algorithm ignores self-loops and parallel edges, since cliques
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are not conventionally defined with such edges.
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References
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----------
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.. [1] Bron, C. and Kerbosch, J.
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"Algorithm 457: finding all cliques of an undirected graph".
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*Communications of the ACM* 16, 9 (Sep. 1973), 575--577.
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<http://portal.acm.org/citation.cfm?doid=362342.362367>
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.. [2] Etsuji Tomita, Akira Tanaka, Haruhisa Takahashi,
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"The worst-case time complexity for generating all maximal
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cliques and computational experiments",
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*Theoretical Computer Science*, Volume 363, Issue 1,
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Computing and Combinatorics,
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10th Annual International Conference on
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Computing and Combinatorics (COCOON 2004), 25 October 2006, Pages 28--42
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<https://doi.org/10.1016/j.tcs.2006.06.015>
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.. [3] F. Cazals, C. Karande,
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"A note on the problem of reporting maximal cliques",
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*Theoretical Computer Science*,
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Volume 407, Issues 1--3, 6 November 2008, Pages 564--568,
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<https://doi.org/10.1016/j.tcs.2008.05.010>
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"""
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if len(G) == 0:
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return
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adj = {u: {v for v in G[u] if v != u} for u in G}
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Q = [None]
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subg = set(G)
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cand = set(G)
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u = max(subg, key=lambda u: len(cand & adj[u]))
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ext_u = cand - adj[u]
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stack = []
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try:
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while True:
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if ext_u:
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q = ext_u.pop()
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cand.remove(q)
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Q[-1] = q
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adj_q = adj[q]
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subg_q = subg & adj_q
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if not subg_q:
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yield Q[:]
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else:
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cand_q = cand & adj_q
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if cand_q:
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stack.append((subg, cand, ext_u))
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Q.append(None)
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subg = subg_q
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cand = cand_q
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u = max(subg, key=lambda u: len(cand & adj[u]))
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ext_u = cand - adj[u]
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else:
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Q.pop()
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subg, cand, ext_u = stack.pop()
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except IndexError:
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pass
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# TODO Should this also be not implemented for directed graphs?
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def find_cliques_recursive(G):
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"""Returns all maximal cliques in a graph.
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For each node *v*, a *maximal clique for v* is a largest complete
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subgraph containing *v*. The largest maximal clique is sometimes
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called the *maximum clique*.
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This function returns an iterator over cliques, each of which is a
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list of nodes. It is a recursive implementation, so may suffer from
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recursion depth issues.
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Parameters
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----------
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G : NetworkX graph
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Returns
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-------
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iterator
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An iterator over maximal cliques, each of which is a list of
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nodes in `G`. The order of cliques is arbitrary.
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See Also
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--------
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find_cliques
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An iterative version of the same algorithm.
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Notes
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-----
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To obtain a list of all maximal cliques, use
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`list(find_cliques_recursive(G))`. However, be aware that in the
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worst-case, the length of this list can be exponential in the number
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of nodes in the graph. This function avoids storing all cliques in memory
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by only keeping current candidate node lists in memory during its search.
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This implementation is based on the algorithm published by Bron and
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Kerbosch (1973) [1]_, as adapted by Tomita, Tanaka and Takahashi
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(2006) [2]_ and discussed in Cazals and Karande (2008) [3]_. For a
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non-recursive implementation, see :func:`find_cliques`.
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This algorithm ignores self-loops and parallel edges, since cliques
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are not conventionally defined with such edges.
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References
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----------
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.. [1] Bron, C. and Kerbosch, J.
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"Algorithm 457: finding all cliques of an undirected graph".
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*Communications of the ACM* 16, 9 (Sep. 1973), 575--577.
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<http://portal.acm.org/citation.cfm?doid=362342.362367>
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.. [2] Etsuji Tomita, Akira Tanaka, Haruhisa Takahashi,
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"The worst-case time complexity for generating all maximal
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cliques and computational experiments",
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*Theoretical Computer Science*, Volume 363, Issue 1,
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Computing and Combinatorics,
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|
10th Annual International Conference on
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Computing and Combinatorics (COCOON 2004), 25 October 2006, Pages 28--42
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<https://doi.org/10.1016/j.tcs.2006.06.015>
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.. [3] F. Cazals, C. Karande,
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"A note on the problem of reporting maximal cliques",
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*Theoretical Computer Science*,
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Volume 407, Issues 1--3, 6 November 2008, Pages 564--568,
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<https://doi.org/10.1016/j.tcs.2008.05.010>
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"""
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if len(G) == 0:
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return iter([])
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adj = {u: {v for v in G[u] if v != u} for u in G}
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Q = []
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def expand(subg, cand):
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u = max(subg, key=lambda u: len(cand & adj[u]))
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for q in cand - adj[u]:
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cand.remove(q)
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Q.append(q)
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adj_q = adj[q]
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subg_q = subg & adj_q
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if not subg_q:
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yield Q[:]
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else:
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cand_q = cand & adj_q
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if cand_q:
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for clique in expand(subg_q, cand_q):
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yield clique
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Q.pop()
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return expand(set(G), set(G))
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def make_max_clique_graph(G, create_using=None):
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"""Returns the maximal clique graph of the given graph.
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The nodes of the maximal clique graph of `G` are the cliques of
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`G` and an edge joins two cliques if the cliques are not disjoint.
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Parameters
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----------
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G : NetworkX graph
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create_using : NetworkX graph constructor, optional (default=nx.Graph)
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Graph type to create. If graph instance, then cleared before populated.
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Returns
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-------
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NetworkX graph
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A graph whose nodes are the cliques of `G` and whose edges
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join two cliques if they are not disjoint.
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Notes
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-----
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This function behaves like the following code::
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import networkx as nx
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G = nx.make_clique_bipartite(G)
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cliques = [v for v in G.nodes() if G.nodes[v]['bipartite'] == 0]
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G = nx.bipartite.project(G, cliques)
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G = nx.relabel_nodes(G, {-v: v - 1 for v in G})
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It should be faster, though, since it skips all the intermediate
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steps.
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"""
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if create_using is None:
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B = G.__class__()
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else:
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B = nx.empty_graph(0, create_using)
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cliques = list(enumerate(set(c) for c in find_cliques(G)))
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# Add a numbered node for each clique.
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B.add_nodes_from(i for i, c in cliques)
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# Join cliques by an edge if they share a node.
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clique_pairs = combinations(cliques, 2)
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B.add_edges_from((i, j) for (i, c1), (j, c2) in clique_pairs if c1 & c2)
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return B
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def make_clique_bipartite(G, fpos=None, create_using=None, name=None):
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"""Returns the bipartite clique graph corresponding to `G`.
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In the returned bipartite graph, the "bottom" nodes are the nodes of
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`G` and the "top" nodes represent the maximal cliques of `G`.
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There is an edge from node *v* to clique *C* in the returned graph
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if and only if *v* is an element of *C*.
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Parameters
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----------
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G : NetworkX graph
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An undirected graph.
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fpos : bool
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If True or not None, the returned graph will have an
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additional attribute, `pos`, a dictionary mapping node to
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position in the Euclidean plane.
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create_using : NetworkX graph constructor, optional (default=nx.Graph)
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Graph type to create. If graph instance, then cleared before populated.
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Returns
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-------
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NetworkX graph
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A bipartite graph whose "bottom" set is the nodes of the graph
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`G`, whose "top" set is the cliques of `G`, and whose edges
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join nodes of `G` to the cliques that contain them.
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The nodes of the graph `G` have the node attribute
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'bipartite' set to 1 and the nodes representing cliques
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have the node attribute 'bipartite' set to 0, as is the
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convention for bipartite graphs in NetworkX.
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"""
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B = nx.empty_graph(0, create_using)
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B.clear()
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# The "bottom" nodes in the bipartite graph are the nodes of the
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# original graph, G.
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B.add_nodes_from(G, bipartite=1)
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for i, cl in enumerate(find_cliques(G)):
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# The "top" nodes in the bipartite graph are the cliques. These
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# nodes get negative numbers as labels.
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name = -i - 1
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B.add_node(name, bipartite=0)
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B.add_edges_from((v, name) for v in cl)
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return B
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def graph_clique_number(G, cliques=None):
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"""Returns the clique number of the graph.
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The *clique number* of a graph is the size of the largest clique in
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the graph.
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Parameters
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----------
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G : NetworkX graph
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An undirected graph.
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cliques : list
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A list of cliques, each of which is itself a list of nodes. If
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not specified, the list of all cliques will be computed, as by
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:func:`find_cliques`.
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Returns
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-------
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int
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The size of the largest clique in `G`.
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Notes
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-----
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You should provide `cliques` if you have already computed the list
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of maximal cliques, in order to avoid an exponential time search for
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maximal cliques.
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"""
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if cliques is None:
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cliques = find_cliques(G)
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if len(G.nodes) < 1:
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return 0
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return max([len(c) for c in cliques] or [1])
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def graph_number_of_cliques(G, cliques=None):
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"""Returns the number of maximal cliques in the graph.
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Parameters
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----------
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G : NetworkX graph
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An undirected graph.
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cliques : list
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A list of cliques, each of which is itself a list of nodes. If
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not specified, the list of all cliques will be computed, as by
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:func:`find_cliques`.
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Returns
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-------
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int
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The number of maximal cliques in `G`.
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Notes
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-----
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You should provide `cliques` if you have already computed the list
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of maximal cliques, in order to avoid an exponential time search for
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maximal cliques.
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"""
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if cliques is None:
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cliques = list(find_cliques(G))
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return len(cliques)
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def node_clique_number(G, nodes=None, cliques=None):
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""" Returns the size of the largest maximal clique containing
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each given node.
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Returns a single or list depending on input nodes.
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Optional list of cliques can be input if already computed.
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"""
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if cliques is None:
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if nodes is not None:
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# Use ego_graph to decrease size of graph
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if isinstance(nodes, list):
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d = {}
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for n in nodes:
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H = nx.ego_graph(G, n)
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d[n] = max((len(c) for c in find_cliques(H)))
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else:
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H = nx.ego_graph(G, nodes)
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d = max((len(c) for c in find_cliques(H)))
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return d
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# nodes is None--find all cliques
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cliques = list(find_cliques(G))
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if nodes is None:
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nodes = list(G.nodes()) # none, get entire graph
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if not isinstance(nodes, list): # check for a list
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v = nodes
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# assume it is a single value
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d = max([len(c) for c in cliques if v in c])
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else:
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d = {}
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for v in nodes:
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d[v] = max([len(c) for c in cliques if v in c])
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return d
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# if nodes is None: # none, use entire graph
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# nodes=G.nodes()
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# elif not isinstance(nodes, list): # check for a list
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# nodes=[nodes] # assume it is a single value
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# if cliques is None:
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# cliques=list(find_cliques(G))
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# d={}
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# for v in nodes:
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# d[v]=max([len(c) for c in cliques if v in c])
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# if nodes in G:
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# return d[v] #return single value
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# return d
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def number_of_cliques(G, nodes=None, cliques=None):
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"""Returns the number of maximal cliques for each node.
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Returns a single or list depending on input nodes.
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Optional list of cliques can be input if already computed.
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"""
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if cliques is None:
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cliques = list(find_cliques(G))
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if nodes is None:
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nodes = list(G.nodes()) # none, get entire graph
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if not isinstance(nodes, list): # check for a list
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v = nodes
|
|
# assume it is a single value
|
|
numcliq = len([1 for c in cliques if v in c])
|
|
else:
|
|
numcliq = {}
|
|
for v in nodes:
|
|
numcliq[v] = len([1 for c in cliques if v in c])
|
|
return numcliq
|
|
|
|
|
|
def cliques_containing_node(G, nodes=None, cliques=None):
|
|
"""Returns a list of cliques containing the given node.
|
|
|
|
Returns a single list or list of lists depending on input nodes.
|
|
Optional list of cliques can be input if already computed.
|
|
"""
|
|
if cliques is None:
|
|
cliques = list(find_cliques(G))
|
|
|
|
if nodes is None:
|
|
nodes = list(G.nodes()) # none, get entire graph
|
|
|
|
if not isinstance(nodes, list): # check for a list
|
|
v = nodes
|
|
# assume it is a single value
|
|
vcliques = [c for c in cliques if v in c]
|
|
else:
|
|
vcliques = {}
|
|
for v in nodes:
|
|
vcliques[v] = [c for c in cliques if v in c]
|
|
return vcliques
|