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# This code is part of Qiskit. | ||
# | ||
# (C) Copyright IBM 2020, 2021. | ||
# | ||
# This code is licensed under the Apache License, Version 2.0. You may | ||
# obtain a copy of this license in the LICENSE.txt file in the root directory | ||
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0. | ||
# | ||
# Any modifications or derivative works of this code must retain this | ||
# copyright notice, and modified files need to carry a notice indicating | ||
# that they have been altered from the originals. | ||
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"""The Gurobi optimizer wrapped to be used within Qiskit's optimization module.""" | ||
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import logging | ||
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from qiskit.exceptions import MissingOptionalLibraryError | ||
from .optimization_algorithm import OptimizationAlgorithm, OptimizationResult | ||
from ..exceptions import QiskitOptimizationError | ||
from ..problems.quadratic_program import QuadraticProgram | ||
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logger = logging.getLogger(__name__) | ||
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try: | ||
import gurobipy as gp | ||
_HAS_GUROBI = True | ||
except ImportError: | ||
_HAS_GUROBI = False | ||
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class GurobiOptimizer(OptimizationAlgorithm): | ||
"""The Gurobi optimizer wrapped as an Qiskit :class:`OptimizationAlgorithm`. | ||
This class provides a wrapper for ``gurobipy`` (https://pypi.gurobi.com) | ||
to be used within the optimization module. | ||
Examples: | ||
>>> from qiskit_optimization.problems import QuadraticProgram | ||
>>> from qiskit_optimization.algorithms import GurobiOptimizer | ||
>>> problem = QuadraticProgram() | ||
>>> # specify problem here, if gurobi is installed | ||
>>> optimizer = GurobiOptimizer() if GurobiOptimizer.is_gurobi_installed() else None | ||
>>> # Suppress gurobipy print info to stdout | ||
>>> import sys | ||
>>> class DevNull: | ||
... def noop(*args, **kwargs): pass | ||
... close = write = flush = writelines = noop | ||
>>> sys.stdout = DevNull() | ||
>>> result = optimizer.solve(problem) | ||
""" | ||
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def __init__(self, disp: bool = False) -> None: | ||
"""Initializes the GurobiOptimizer. | ||
Args: | ||
disp: Whether to print Gurobi output or not. | ||
Raises: | ||
MissingOptionalLibraryError: Gurobi is not installed. | ||
""" | ||
if not _HAS_GUROBI: | ||
raise MissingOptionalLibraryError( | ||
libname='GUROBI', | ||
name='GurobiOptimizer', | ||
pip_install="pip install -i https://pypi.gurobi.com gurobipy") | ||
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self._disp = disp | ||
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@staticmethod | ||
def is_gurobi_installed(): | ||
""" Returns True if gurobi is installed """ | ||
return _HAS_GUROBI | ||
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@property | ||
def disp(self) -> bool: | ||
"""Returns the display setting. | ||
Returns: | ||
Whether to print Gurobi information or not. | ||
""" | ||
return self._disp | ||
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@disp.setter | ||
def disp(self, disp: bool): | ||
"""Set the display setting. | ||
Args: | ||
disp: The display setting. | ||
""" | ||
self._disp = disp | ||
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# pylint:disable=unused-argument | ||
def get_compatibility_msg(self, problem: QuadraticProgram) -> str: | ||
"""Checks whether a given problem can be solved with this optimizer. | ||
Returns ``''`` since Gurobi accepts all problems that can be modeled using the | ||
``QuadraticProgram``. Gurobi will also solve non-convex problems. | ||
Args: | ||
problem: The optimization problem to check compatibility. | ||
Returns: | ||
An empty string. | ||
""" | ||
return '' | ||
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def solve(self, problem: QuadraticProgram) -> OptimizationResult: | ||
"""Tries to solves the given problem using the optimizer. | ||
Runs the optimizer to try to solve the optimization problem. If problem is not convex, | ||
this optimizer may raise an exception due to incompatibility, depending on the settings. | ||
Args: | ||
problem: The problem to be solved. | ||
Returns: | ||
The result of the optimizer applied to the problem. | ||
Raises: | ||
QiskitOptimizationError: If the problem is incompatible with the optimizer. | ||
""" | ||
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# convert to Gurobi problem | ||
model = problem.to_gurobipy() | ||
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# Enable non-convex | ||
model.Params.NonConvex = 2 | ||
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# set display setting | ||
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if not self.disp: | ||
model.Params.OutputFlag = 0 | ||
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# solve problem | ||
try: | ||
model.optimize() | ||
except gp.GurobiError as ex: | ||
raise QiskitOptimizationError(str(ex)) from ex | ||
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# create results | ||
result = OptimizationResult(x=model.X, fval=model.ObjVal, | ||
variables=problem.variables, | ||
status=self._get_feasibility_status(problem, model.X), | ||
raw_results=model) | ||
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# return solution | ||
return result |
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