def test_embed_bqm_BINARY(self):
Q = {
('a', 'a'): 0,
('a', 'b'): -1,
('b', 'b'): 0,
('c', 'c'): 0,
('b', 'c'): -1
}
bqm = dimod.BinaryQuadraticModel.from_qubo(Q)
embedding = {'a': {0}, 'b': {1}, 'c': {2, 3}}
embedded_bqm = dwave.embedding.embed_bqm(bqm,
embedding,
nx.cycle_graph(4),
chain_strength=1)
# check that the energy has been preserved
for config in itertools.product((0, 1), repeat=3):
sample = dict(zip(('a', 'b', 'c'), config))
target_sample = {
u: sample[v]
for v, chain in embedding.items() for u in chain
} # no chains broken
self.assertAlmostEqual(bqm.energy(sample),
embedded_bqm.energy(target_sample))
def sample(self, bqm, **kwargs):
"""Sample from the specified binary quadratic model.
Args:
bqm (:obj:`dimod.BinaryQuadraticModel`):
Binary quadratic model to be sampled from.
**kwargs:
Optional keyword arguments for the sampling method, specified per solver.
Returns:
:class:`dimod.SampleSet`
Examples:
This example submits a simple Ising problem of just two variables on a
D-Wave system.
Because the problem fits in a single :term:`Chimera` unit cell, it is tiled
across the solver's entire Chimera graph, resulting in multiple samples
(the exact number depends on the working Chimera graph of the D-Wave system).
>>> from dwave.system import DWaveSampler, EmbeddingComposite
>>> from dwave.system import TilingComposite
...
>>> qpu_2000q = DWaveSampler(solver={'topology__type': 'chimera'})
>>> sampler = EmbeddingComposite(TilingComposite(qpu_2000q, 1, 1, 4))
>>> response = sampler.sample_ising({},{('a', 'b'): 1})
>>> len(response) # doctest: +SKIP
246
See `Ocean Glossary <https://docs.ocean.dwavesys.com/en/stable/concepts/index.html>`_
for explanations of technical terms in descriptions of Ocean tools.
"""
# apply the embeddings to the given problem to tile it across the child sampler
embedded_bqm = dimod.BinaryQuadraticModel.empty(bqm.vartype)
__, __, target_adjacency = self.child.structure
for embedding in self.embeddings:
embedded_bqm.update(
dwave.embedding.embed_bqm(bqm, embedding, target_adjacency))
# solve the problem on the child system
tiled_response = self.child.sample(embedded_bqm, **kwargs)
responses = []
for embedding in self.embeddings:
embedding = {
v: chain
for v, chain in embedding.items() if v in bqm.variables
}
responses.append(
dwave.embedding.unembed_sampleset(tiled_response, embedding,
bqm))
answer = dimod.concatenate(responses)
answer.info.update(tiled_response.info)
return answer
def test_embedding_with_extra_chains(self):
embedding = {0: [0, 1], 1: [2], 2: [3]}
G = nx.cycle_graph(4)
bqm = dimod.BinaryQuadraticModel.from_qubo({(0, 0): 1})
target_bqm = dwave.embedding.embed_bqm(bqm, embedding, G)
for v, c in embedding.items():
if v in bqm.variables:
for q in c:
self.assertIn(q, target_bqm)
else:
for q in c:
self.assertNotIn(q, target_bqm)
def test_embed_bqm_NAE3SAT_to_square(self):
h = {'a': 0, 'b': 0, 'c': 0}
J = {('a', 'b'): 1, ('b', 'c'): 1, ('a', 'c'): 1}
bqm = dimod.BinaryQuadraticModel.from_ising(h, J)
embedding = {'a': {0}, 'b': {1}, 'c': {2, 3}}
embedded_bqm = dwave.embedding.embed_bqm(bqm,
embedding,
nx.cycle_graph(4),
chain_strength=1)
self.assertEqual(
embedded_bqm,
dimod.BinaryQuadraticModel(
{
0: 0,
1: 0,
2: 0,
3: 0
},
{
(0, 1): 1,
(1, 2): 1,
(2, 3): -1,
(0, 3): 1
},
1.0, # offset the energy from satisfying chains
dimod.SPIN))
# check that the energy has been preserved
for config in itertools.product((-1, 1), repeat=3):
sample = dict(zip(('a', 'b', 'c'), config))
target_sample = {
u: sample[v]
for v, chain in embedding.items() for u in chain
} # no chains broken
self.assertAlmostEqual(bqm.energy(sample),
embedded_bqm.energy(target_sample))
