def sample_markov_network(MN, sampler=None, fixed_variables=None,
return_sampleset=False,
**sampler_args):
bqm = markov_network_bqm(MN)
# use the FixedVar
fv_sampler = dimod.FixedVariableComposite(sampler)
sampleset = fv_sampler.sample(bqm, fixed_variables=fixed_variables,
**sampler_args)
if return_sampleset:
return sampleset
else:
return list(map(dict, sampleset.samples()))
def sample_markov_network(MN, sampler=None, fixed_variables=None,
return_sampleset=False,
**sampler_args):
"""Samples from a markov network using the provided sampler.
Parameters
----------
G : NetworkX graph
A Markov Network as returned by :func:`.markov_network`
sampler
A binary quadratic model sampler. A sampler is a process that
samples from low energy states in models defined by an Ising
equation or a Quadratic Unconstrained Binary Optimization
Problem (QUBO). A sampler is expected to have a 'sample_qubo'
and 'sample_ising' method. A sampler is expected to return an
iterable of samples, in order of increasing energy. If no
sampler is provided, one must be provided using the
`set_default_sampler` function.
fixed_variables : dict
A dictionary of variable assignments to be fixed in the markov network.
return_sampleset : bool (optional, default=False)
If True, returns a :obj:`dimod.SampleSet` rather than a list of samples.
**sampler_args
Additional keyword parameters are passed to the sampler.
Returns
-------
samples : list[dict]/:obj:`dimod.SampleSet`
A list of samples ordered from low-to-high energy or a sample set.
Examples
--------
>>> import dimod
...
>>> potentials = {('a', 'b'): {(0, 0): -1,
... (0, 1): .5,
... (1, 0): .5,
... (1, 1): 2}}
>>> MN = dnx.markov_network(potentials)
>>> sampler = dimod.ExactSolver()
>>> samples = dnx.sample_markov_network(MN, sampler)
>>> samples[0]
{'a': 0, 'b': 0}
>>> import dimod
...
>>> potentials = {('a', 'b'): {(0, 0): -1,
... (0, 1): .5,
... (1, 0): .5,
... (1, 1): 2}}
>>> MN = dnx.markov_network(potentials)
>>> sampler = dimod.ExactSolver()
>>> samples = dnx.sample_markov_network(MN, sampler, return_sampleset=True)
>>> samples.first
Sample(sample={'a': 0, 'b': 0}, energy=-1.0, num_occurrences=1)
>>> import dimod
...
>>> potentials = {('a', 'b'): {(0, 0): -1,
... (0, 1): .5,
... (1, 0): .5,
... (1, 1): 2},
... ('b', 'c'): {(0, 0): -9,
... (0, 1): 1.2,
... (1, 0): 7.2,
... (1, 1): 5}}
>>> MN = dnx.markov_network(potentials)
>>> sampler = dimod.ExactSolver()
>>> samples = dnx.sample_markov_network(MN, sampler, fixed_variables={'b': 0})
>>> samples[0]
{'a': 0, 'c': 0, 'b': 0}
Notes
-----
Samplers by their nature may not return the optimal solution. This
function does not attempt to confirm the quality of the returned
sample.
"""
bqm = markov_network_bqm(MN)
# use the FixedVar
fv_sampler = dimod.FixedVariableComposite(sampler)
sampleset = fv_sampler.sample(bqm, fixed_variables=fixed_variables,
**sampler_args)
if return_sampleset:
return sampleset
else:
return list(map(dict, sampleset.samples()))