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traversal.py
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traversal.py
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# The following traversal code is adapted from NetworkX's implementation. The
# only thing that was preventing their implementation from using BQMs directly
# was the not_implemented_for decorator. So rather than force the construction
# of a new NetworkX graph, we just skip that decorator (and make some other
# small changes). Modifications are licensed under the Apache 2.0 Software
# license at the top.
#
# Copyright 2019 D-Wave Systems Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# NetworkX license:
#
# Copyright (C) 2004-2019, NetworkX Developers
# Aric Hagberg <hagberg@lanl.gov>
# Dan Schult <dschult@colgate.edu>
# Pieter Swart <swart@lanl.gov>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#
# * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following
# disclaimer in the documentation and/or other materials provided
# with the distribution.
#
# * Neither the name of the NetworkX Developers nor the names of its
# contributors may be used to endorse or promote products derived
# from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
def connected_components(bqm):
"""Yields sets of connected variables.
Args:
bqm (:obj:`dimod.BinaryQuadraticModel`):
A binary quadratic model (BQM).
Yields:
set: A set of variables in the BQM that form a connected component.
"""
seen = set()
for v in bqm.variables:
if v not in seen:
c = set(bfs_variables(bqm, v))
yield c
seen.update(c)
def bfs_variables(bqm, source):
"""Yields variables in breadth-first search order.
Args:
bqm (:obj:`dimod.BinaryQuadraticModel`):
A binary quadratic model.
source (variable):
A variable in the binary quadratic model (BQM).
Yields:
variable: variables in the BQM, yielded in breadth-first search order
starting at source.
"""
seen = set()
nextlevel = {source}
while nextlevel:
thislevel = nextlevel
nextlevel = set()
for v in thislevel:
if v not in seen:
yield v
seen.add(v)
nextlevel.update(bqm.adj[v])