Add DWaveCliqueSampler

docs/reference/samplers.rst

@@ -42,6 +42,34 @@ Methods
    DWaveSampler.sample_qubo
    DWaveSampler.validate_anneal_schedule
 
+DWaveCliqueSampler
+==================
+
+.. autoclass:: DWaveCliqueSampler
+
+Properties
+----------
+
+.. autosummary::
+   :toctree: generated/
+
+   DWaveCliqueSampler.largest_clique_size
+   DWaveCliqueSampler.properties
+   DWaveCliqueSampler.parameters
+
+
+Methods
+-------
+
+.. autosummary::
+   :toctree: generated/
+
+   DWaveCliqueSampler.largest_clique
+   DWaveCliqueSampler.sample
+   DWaveCliqueSampler.sample_ising
+   DWaveCliqueSampler.sample_qubo
+
+
 LeapHybridSampler
 =================
 

dwave/system/samplers/__init__.py

@@ -11,7 +11,7 @@
 #    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.
-#
-# ================================================================================================
+
+from dwave.system.samplers.clique import *
 from dwave.system.samplers.dwave_sampler import *
 from dwave.system.samplers.leap_hybrid_sampler import *

dwave/system/samplers/clique.py

@@ -0,0 +1,197 @@
+# Copyright 2020 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.
+
+import math
+
+import dimod
+import dwave_networkx as dnx
+
+from minorminer.busclique import find_clique_embedding, busgraph_cache
+
+from dwave.system.samplers.dwave_sampler import DWaveSampler
+
+__all__ = ['DWaveCliqueSampler']
+
+
+class DWaveCliqueSampler(dimod.Sampler):
+    """A sampler for solving clique problems on the D-Wave system.
+
+    The `DWaveCliqueSampler` wraps
+    :func:`minorminer.busclique.find_clique_embedding` to generate embeddings
+    with even chain length. These embeddings will work well for dense
+    binary quadratic models. For sparse models, using
+    :class:`.EmbeddingComposite` with :class:`.DWaveSampler` is preferred.
+
+    Args:
+        **config:
+            Keyword arguments, as accepted by :class:`.DWaveSampler`
+
+    """
+    def __init__(self, **config):
+
+        # get the QPU with the most qubits available, subject to other
+        # constraints specified in **config
+        self.child = child = DWaveSampler(order_by='-num_active_qubits',
+                                          **config)
+
+        # do some topology checking
+        try:
+            topology_type = child.properties['topology']['type']
+            shape = child.properties['topology']['shape']
+        except KeyError:
+            raise ValueError("given sampler has unknown topology format")
+
+        # We need a networkx graph with certain properties. In the
+        # future it would be good for DWaveSampler to handle this.
+        # See https://github.com/dwavesystems/dimod/issues/647
+        if topology_type == 'chimera':
+            G = dnx.chimera_graph(*shape,
+                                  node_list=child.nodelist,
+                                  edge_list=child.edgelist,
+                                  )
+        elif topology_type == 'pegasus':
+            G = dnx.pegasus_graph(shape[0],
+                                  node_list=child.nodelist,
+                                  edge_list=child.edgelist,
+                                  )
+        else:
+            raise ValueError("unknown topology type")
+
+        self.target_graph = G
+
+        # get the energy range
+        self.qpu_linear_range = child.properties['h_range']
+        self.qpu_quadratic_range = child.properties.get(
+            'extended_j_range', child.properties['j_range'])
+
+    @property
+    def parameters(self):
+        try:
+            return self._parameters
+        except AttributeError:
+            pass
+
+        self._parameters = parameters = self.child.parameters.copy()
+
+        # this sampler handles scaling
+        parameters.pop('auto_scale', None)
+        parameters.pop('bias_range', None)
+        parameters.pop('quadratic_range', None)
+
+        return parameters
+
+    @property
+    def properties(self):
+        try:
+            return self._properties
+        except AttributeError:
+            pass
+
+        self._properties = dict(qpu_properties=self.child.properties)
+        return self.properties
+
+    @property
+    def largest_clique_size(self):
+        """The maximum number of variables."""
+        return len(self.largest_clique())
+
+    def largest_clique(self):
+        """Return a largest-size clique embedding."""
+        return busgraph_cache(self.target_graph).largest_clique()
+
+    def sample(self, bqm, chain_strength=None, **kwargs):
+        """Sample from the specified binary quadratic model.
+
+        Args:
+            bqm (:class:`~dimod.BinaryQuadraticModel`):
+                Any binary quadratic model with up to
+                :attr:`.largest_clique_size` variables. This BQM is embedded
+                using a dense clique embedding.
+
+            chain_strength (float, optional):
+                The (relative) chain strength to use in the embedding. By
+                default a chain strength of `1.5sqrt(N)` where `N` is the size
+                of the largest clique, as returned by
+                :attr:`.largest_clique_size`.
+
+            **kwargs:
+                Optional keyword arguments for the sampling method, specified
+                per solver in :attr:`.DWaveCliqueSampler.parameters`.
+                D-Wave System Documentation's
+                `solver guide <https://docs.dwavesys.com/docs/latest/doc_solver_ref.html>`_
+                describes the parameters and properties supported on the D-Wave
+                system. Note that `auto_scale` is not supported by this
+                sampler, because it scales the problem as part of the embedding
+                process.
+
+        """
+
+        # some arguments should not be overwritten
+        if 'auto_scale' in kwargs:
+            raise TypeError("sample() got an unexpected keyword argument "
+                            "'auto_scale'")
+        if 'bias_range' in kwargs:
+            raise TypeError("sample() got an unexpected keyword argument "
+                            "'bias_range'")
+        if 'quadratic_range' in kwargs:
+            raise TypeError("sample() got an unexpected keyword argument "
+                            "'quadratic_range'")
+
+        # handle circular import. todo: fix
+        from dwave.system.composites.embedding import FixedEmbeddingComposite
+
+        # get the embedding
+        embedding = find_clique_embedding(bqm.variables, self.target_graph,
+                                          use_cache=True)
+
+        # returns an empty embedding when the BQM is too large
+        if not embedding and bqm.num_variables:
+            raise ValueError("Cannot embed given BQM (size {}), sampler can "
+                             "only handle problems of size {}".format(
+                                len(bqm.variables), self.largest_clique_size))
+
+        assert bqm.num_variables == len(embedding)  # sanity check
+
+        if chain_strength is None:
+            # chain length determines chain strength
+            if embedding:
+                chain_strength = 1.5 * math.sqrt(len(embedding))
+            else:
+                chain_strength = 1  # doesn't matter
+
+            # scale chain strength by the problem scale
+            scalar = max(max(map(abs, bqm.linear.values()), default=0),
+                         max(map(abs, bqm.quadratic.values()), default=0))
+            chain_strength *= scalar
+
+        # # scaling only make sense in Ising space
+        original_bqm = bqm
+
+        if bqm.vartype is not dimod.SPIN:
+            bqm = bqm.change_vartype(dimod.SPIN, inplace=False)
+
+        sampler = FixedEmbeddingComposite(
+            dimod.ScaleComposite(self.child),
+            embedding)
+
+        sampleset = sampler.sample(bqm,
+                                   bias_range=self.qpu_linear_range,
+                                   quadratic_range=self.qpu_quadratic_range,
+                                   auto_scale=False,
+                                   chain_strength=chain_strength,
+                                   **kwargs
+                                   )
+
+        # change_vartype is non-blocking
+        return sampleset.change_vartype(original_bqm.vartype)

dwave/system/samplers/dwave_sampler.py

@@ -105,6 +105,12 @@ class DWaveSampler(dimod.Sampler, dimod.Structured):
             then it will instead propogate the `SolverNotFoundError` to the
             user.
 
+        order_by (callable/str/None):
+            Solver sorting key function or (or :class:`~dwave.cloud.Solver`
+            attribute/item dot-separated path).
+            See :class:`~dwave.cloud.Client.get_solvers` for a more detailed
+            description of the parameter.
+
         config_file (str, optional):
             Path to a configuration file that identifies a D-Wave system and provides
             connection information.
@@ -151,7 +157,7 @@ class DWaveSampler(dimod.Sampler, dimod.Structured):
     for explanations of technical terms in descriptions of Ocean tools.
 
     """
-    def __init__(self, failover=False, retry_interval=-1, **config):
+    def __init__(self, failover=False, retry_interval=-1, order_by=None, **config):
 
         if config.get('solver_features') is not None:
             warn("'solver_features' argument has been renamed to 'solver'.", DeprecationWarning)
@@ -162,7 +168,12 @@ def __init__(self, failover=False, retry_interval=-1, **config):
             config['solver'] = config.pop('solver_features')
 
         self.client = Client.from_config(**config)
-        self.solver = self.client.get_solver()
+
+        if order_by is None:
+            # use the default from the cloud-client
+            self.solver = self.client.get_solver()
+        else:
+            self.solver = self.client.get_solver(order_by=order_by)
 
         self.failover = failover
         self.retry_interval = retry_interval

requirements.txt

@@ -1,12 +1,12 @@
 --extra-index-url https://pypi.dwavesys.com/simple
 
-dimod==0.9.1
-dwave-cloud-client==0.7.2
+dimod==0.9.5
+dwave-cloud-client==0.7.5
 dwave-networkx==0.8.4
 dwave-drivers==0.4.4
 dwave-tabu==0.2.2
 homebase==1.0.1
-minorminer==0.1.9
+minorminer==0.2.0
 six==1.11.0
 mock==2.0.0
 numpy==1.18.0

setup.py

@@ -25,12 +25,12 @@
 exec(open(os.path.join(".", "dwave", "system", "package_info.py")).read())
 
 
-install_requires = ['dimod>=0.9.0,<0.10.0',
-                    'dwave-cloud-client>=0.7.2,<0.8.0',
+install_requires = ['dimod>=0.9.5,<0.10.0',
+                    'dwave-cloud-client>=0.7.5,<0.8.0',
                     'dwave-networkx>=0.8.4',
                     'networkx>=2.0,<3.0',
                     'homebase>=1.0.0,<2.0.0',
-                    'minorminer>=0.1.3,<0.2.0',
+                    'minorminer>=0.2.0,<0.3.0',
                     'six>=1.11.0,<2.0.0',
                     'numpy>=1.14.0,<2.0.0',
                     'dwave-tabu>=0.2.0',

tests/qpu/test_dwavecliquesampler.py

@@ -0,0 +1,55 @@
+# Copyright 2020 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.
+
+import itertools
+import unittest
+
+import dimod
+
+from dwave.cloud.exceptions import ConfigFileError, SolverNotFoundError
+from dwave.system import DWaveCliqueSampler
+
+
+class TestDWaveCliqueSampler(unittest.TestCase):
+    def test_chimera(self):
+        try:
+            sampler = DWaveCliqueSampler(
+                solver=dict(topology__type='chimera', qpu=True))
+        except (ValueError, ConfigFileError, SolverNotFoundError):
+            raise unittest.SkipTest("no Chimera-structured QPU available")
+
+        dimod.testing.assert_sampler_api(sampler)
+
+        # submit a maximum ferromagnet
+        bqm = dimod.AdjVectorBQM('SPIN')
+        for u, v in itertools.combinations(sampler.largest_clique(), 2):
+            bqm.quadratic[u, v] = -1
+
+        sampler.sample(bqm).resolve()
+
+    def test_pegasus(self):
+        try:
+            sampler = DWaveCliqueSampler(
+                solver=dict(topology__type='pegasus', qpu=True))
+        except (ValueError, ConfigFileError, SolverNotFoundError):
+            raise unittest.SkipTest("no Pegasus-structured QPU available")
+
+        dimod.testing.assert_sampler_api(sampler)
+
+        # submit a maximum ferromagnet
+        bqm = dimod.AdjVectorBQM('SPIN')
+        for u, v in itertools.combinations(sampler.largest_clique(), 2):
+            bqm.quadratic[u, v] = -1
+
+        sampler.sample(bqm).resolve()