Module miplearn.solvers.learning
Expand source code
# MIPLearn: Extensible Framework for Learning-Enhanced Mixed-Integer Optimization
# Copyright (C) 2020, UChicago Argonne, LLC. All rights reserved.
# Released under the modified BSD license. See COPYING.md for more details.
import gzip
import logging
import os
import pickle
import tempfile
from typing import Optional, List, Any, IO, cast, BinaryIO, Union, Callable, Dict
from p_tqdm import p_map
from miplearn.components.component import Component
from miplearn.components.cuts import UserCutsComponent
from miplearn.components.lazy_dynamic import DynamicLazyConstraintsComponent
from miplearn.components.objective import ObjectiveValueComponent
from miplearn.components.primal import PrimalSolutionComponent
from miplearn.instance import Instance
from miplearn.solvers import _RedirectOutput
from miplearn.solvers.internal import InternalSolver
from miplearn.solvers.pyomo.gurobi import GurobiPyomoSolver
from miplearn.types import MIPSolveStats, TrainingSample
logger = logging.getLogger(__name__)
class _GlobalVariables:
def __init__(self) -> None:
self.solver: Optional[LearningSolver] = None
self.instances: Optional[Union[List[str], List[Instance]]] = None
self.output_filenames: Optional[List[str]] = None
self.discard_outputs: bool = False
# Global variables used for multiprocessing. Global variables are copied by the
# operating system when the process forks. Local variables are copied through
# serialization, which is a much slower process.
_GLOBAL = [_GlobalVariables()]
def _parallel_solve(idx):
solver = _GLOBAL[0].solver
instances = _GLOBAL[0].instances
output_filenames = _GLOBAL[0].output_filenames
discard_outputs = _GLOBAL[0].discard_outputs
if output_filenames is None:
output_filename = None
else:
output_filename = output_filenames[idx]
stats = solver.solve(
instances[idx],
output_filename=output_filename,
discard_output=discard_outputs,
)
return stats, instances[idx]
class LearningSolver:
"""
Mixed-Integer Linear Programming (MIP) solver that extracts information
from previous runs and uses Machine Learning methods to accelerate the
solution of new (yet unseen) instances.
Parameters
----------
components: List[Component]
Set of components in the solver. By default, includes
`ObjectiveValueComponent`, `PrimalSolutionComponent`,
`DynamicLazyConstraintsComponent` and `UserCutsComponent`.
mode: str
If "exact", solves problem to optimality, keeping all optimality
guarantees provided by the MIP solver. If "heuristic", uses machine
learning more aggressively, and may return suboptimal solutions.
solver: Callable[[], InternalSolver]
A callable that constructs the internal solver. If None is provided,
use GurobiPyomoSolver.
use_lazy_cb: bool
If true, use native solver callbacks for enforcing lazy constraints,
instead of a simple loop. May not be supported by all solvers.
solve_lp_first: bool
If true, solve LP relaxation first, then solve original MILP. This
option should be activated if the LP relaxation is not very
expensive to solve and if it provides good hints for the integer
solution.
simulate_perfect: bool
If true, each call to solve actually performs three actions: solve
the original problem, train the ML models on the data that was just
collected, and solve the problem again. This is useful for evaluating
the theoretical performance of perfect ML models.
"""
def __init__(
self,
components: List[Component] = None,
mode: str = "exact",
solver: Callable[[], InternalSolver] = None,
use_lazy_cb: bool = False,
solve_lp_first: bool = True,
simulate_perfect: bool = False,
):
if solver is None:
solver = GurobiPyomoSolver
assert callable(solver), f"Callable expected. Found {solver.__class__} instead."
self.components: Dict[str, Component] = {}
self.internal_solver: Optional[InternalSolver] = None
self.mode: str = mode
self.simulate_perfect: bool = simulate_perfect
self.solve_lp_first: bool = solve_lp_first
self.solver_factory: Callable[[], InternalSolver] = solver
self.tee = False
self.use_lazy_cb: bool = use_lazy_cb
if components is not None:
for comp in components:
self._add_component(comp)
else:
self._add_component(ObjectiveValueComponent())
self._add_component(PrimalSolutionComponent(mode=mode))
self._add_component(DynamicLazyConstraintsComponent())
self._add_component(UserCutsComponent())
assert self.mode in ["exact", "heuristic"]
def _solve(
self,
instance: Union[Instance, str],
model: Any = None,
output_filename: Optional[str] = None,
discard_output: bool = False,
tee: bool = False,
) -> MIPSolveStats:
# Load instance from file, if necessary
filename = None
fileformat = None
file: Union[BinaryIO, gzip.GzipFile]
if isinstance(instance, str):
filename = instance
logger.info("Reading: %s" % filename)
if filename.endswith(".gz"):
fileformat = "pickle-gz"
with gzip.GzipFile(filename, "rb") as file:
instance = pickle.load(cast(IO[bytes], file))
else:
fileformat = "pickle"
with open(filename, "rb") as file:
instance = pickle.load(cast(IO[bytes], file))
assert isinstance(instance, Instance)
# Generate model
if model is None:
with _RedirectOutput([]):
model = instance.to_model()
# Initialize training sample
training_sample: TrainingSample = {}
if not hasattr(instance, "training_data"):
instance.training_data = []
instance.training_data += [training_sample]
# Initialize internal solver
self.tee = tee
self.internal_solver = self.solver_factory()
assert self.internal_solver is not None
assert isinstance(self.internal_solver, InternalSolver)
self.internal_solver.set_instance(instance, model)
# Solve linear relaxation
if self.solve_lp_first:
logger.info("Solving LP relaxation...")
lp_stats = self.internal_solver.solve_lp(tee=tee)
training_sample["LP solution"] = self.internal_solver.get_solution()
training_sample["LP value"] = lp_stats["Optimal value"]
training_sample["LP log"] = lp_stats["Log"]
else:
training_sample["LP solution"] = self.internal_solver.get_empty_solution()
training_sample["LP value"] = 0.0
# Before-solve callbacks
logger.debug("Running before_solve callbacks...")
for component in self.components.values():
component.before_solve(self, instance, model)
# Define wrappers
def iteration_cb_wrapper() -> bool:
should_repeat = False
assert isinstance(instance, Instance)
for comp in self.components.values():
if comp.iteration_cb(self, instance, model):
should_repeat = True
return should_repeat
def lazy_cb_wrapper(
cb_solver: LearningSolver,
cb_model: Any,
) -> None:
assert isinstance(instance, Instance)
for comp in self.components.values():
comp.lazy_cb(self, instance, model)
lazy_cb = None
if self.use_lazy_cb:
lazy_cb = lazy_cb_wrapper
# Solve MILP
logger.info("Solving MILP...")
stats = self.internal_solver.solve(
tee=tee,
iteration_cb=iteration_cb_wrapper,
lazy_cb=lazy_cb,
)
if "LP value" in training_sample.keys():
stats["LP value"] = training_sample["LP value"]
# Read MIP solution and bounds
training_sample["Lower bound"] = stats["Lower bound"]
training_sample["Upper bound"] = stats["Upper bound"]
training_sample["MIP log"] = stats["Log"]
training_sample["Solution"] = self.internal_solver.get_solution()
# After-solve callbacks
logger.debug("Calling after_solve callbacks...")
for component in self.components.values():
component.after_solve(self, instance, model, stats, training_sample)
# Write to file, if necessary
if not discard_output and filename is not None:
if output_filename is None:
output_filename = filename
logger.info("Writing: %s" % output_filename)
if fileformat == "pickle":
with open(output_filename, "wb") as file:
pickle.dump(instance, cast(IO[bytes], file))
else:
with gzip.GzipFile(output_filename, "wb") as file:
pickle.dump(instance, cast(IO[bytes], file))
return stats
def solve(
self,
instance: Union[Instance, str],
model: Any = None,
output_filename: Optional[str] = None,
discard_output: bool = False,
tee: bool = False,
) -> MIPSolveStats:
"""
Solves the given instance. If trained machine-learning models are
available, they will be used to accelerate the solution process.
The argument `instance` may be either an Instance object or a
filename pointing to a pickled Instance object.
This method adds a new training sample to `instance.training_sample`.
If a filename is provided, then the file is modified in-place. That is,
the original file is overwritten.
If `solver.solve_lp_first` is False, the properties lp_solution and
lp_value will be set to dummy values.
Parameters
----------
instance: Union[Instance, str]
The instance to be solved, or a filename.
model: Any
The corresponding Pyomo model. If not provided, it will be created.
output_filename: Optional[str]
If instance is a filename and output_filename is provided, write the
modified instance to this file, instead of replacing the original one. If
output_filename is None (the default), modified the original file in-place.
discard_output: bool
If True, do not write the modified instances anywhere; simply discard
them. Useful during benchmarking.
tee: bool
If true, prints solver log to screen.
Returns
-------
MIPSolveStats
A dictionary of solver statistics containing at least the following
keys: "Lower bound", "Upper bound", "Wallclock time", "Nodes",
"Sense", "Log", "Warm start value" and "LP value".
Additional components may generate additional keys. For example,
ObjectiveValueComponent adds the keys "Predicted LB" and
"Predicted UB". See the documentation of each component for more
details.
"""
if self.simulate_perfect:
if not isinstance(instance, str):
raise Exception("Not implemented")
with tempfile.NamedTemporaryFile(suffix=os.path.basename(instance)) as tmp:
self._solve(
instance=instance,
model=model,
output_filename=tmp.name,
tee=tee,
)
self.fit([tmp.name])
return self._solve(
instance=instance,
model=model,
output_filename=output_filename,
discard_output=discard_output,
tee=tee,
)
def parallel_solve(
self,
instances: Union[List[str], List[Instance]],
n_jobs: int = 4,
label: str = "Solve",
output_filenames: Optional[List[str]] = None,
discard_outputs: bool = False,
) -> List[MIPSolveStats]:
"""
Solves multiple instances in parallel.
This method is equivalent to calling `solve` for each item on the list,
but it processes multiple instances at the same time. Like `solve`, this
method modifies each instance in place. Also like `solve`, a list of
filenames may be provided.
Parameters
----------
output_filenames: Optional[List[str]]
If instances are file names and output_filenames is provided, write the
modified instances to these files, instead of replacing the original
files. If output_filenames is None, modifies the instances in-place.
discard_outputs: bool
If True, do not write the modified instances anywhere; simply discard
them instead. Useful during benchmarking.
label: str
Label to show in the progress bar.
instances: Union[List[str], List[Instance]]
The instances to be solved
n_jobs: int
Number of instances to solve in parallel at a time.
Returns
-------
List[MIPSolveStats]
List of solver statistics, with one entry for each provided instance.
The list is the same you would obtain by calling
`[solver.solve(p) for p in instances]`
"""
self.internal_solver = None
self._silence_miplearn_logger()
_GLOBAL[0].solver = self
_GLOBAL[0].output_filenames = output_filenames
_GLOBAL[0].instances = instances
_GLOBAL[0].discard_outputs = discard_outputs
results = p_map(
_parallel_solve,
list(range(len(instances))),
num_cpus=n_jobs,
desc=label,
)
stats = []
for (idx, (s, instance)) in enumerate(results):
stats.append(s)
instances[idx] = instance
self._restore_miplearn_logger()
return stats
def fit(self, training_instances: Union[List[str], List[Instance]]) -> None:
if len(training_instances) == 0:
return
for component in self.components.values():
component.fit(training_instances)
def _add_component(self, component: Component) -> None:
name = component.__class__.__name__
self.components[name] = component
def _silence_miplearn_logger(self) -> None:
miplearn_logger = logging.getLogger("miplearn")
self.prev_log_level = miplearn_logger.getEffectiveLevel()
miplearn_logger.setLevel(logging.WARNING)
def _restore_miplearn_logger(self) -> None:
miplearn_logger = logging.getLogger("miplearn")
miplearn_logger.setLevel(self.prev_log_level)
def __getstate__(self) -> Dict:
self.internal_solver = None
return self.__dict__Classes
class LearningSolver (components=None, mode='exact', solver=None, use_lazy_cb=False, solve_lp_first=True, simulate_perfect=False)-
Mixed-Integer Linear Programming (MIP) solver that extracts information from previous runs and uses Machine Learning methods to accelerate the solution of new (yet unseen) instances.
Parameters
components:List[Component]- Set of components in the solver. By default, includes
ObjectiveValueComponent,PrimalSolutionComponent,DynamicLazyConstraintsComponentandUserCutsComponent. mode:str- If "exact", solves problem to optimality, keeping all optimality guarantees provided by the MIP solver. If "heuristic", uses machine learning more aggressively, and may return suboptimal solutions.
solver:Callable[[],InternalSolver]- A callable that constructs the internal solver. If None is provided, use GurobiPyomoSolver.
use_lazy_cb:bool- If true, use native solver callbacks for enforcing lazy constraints, instead of a simple loop. May not be supported by all solvers.
solve_lp_first:bool- If true, solve LP relaxation first, then solve original MILP. This option should be activated if the LP relaxation is not very expensive to solve and if it provides good hints for the integer solution.
simulate_perfect:bool- If true, each call to solve actually performs three actions: solve the original problem, train the ML models on the data that was just collected, and solve the problem again. This is useful for evaluating the theoretical performance of perfect ML models.
Expand source code
class LearningSolver: """ Mixed-Integer Linear Programming (MIP) solver that extracts information from previous runs and uses Machine Learning methods to accelerate the solution of new (yet unseen) instances. Parameters ---------- components: List[Component] Set of components in the solver. By default, includes `ObjectiveValueComponent`, `PrimalSolutionComponent`, `DynamicLazyConstraintsComponent` and `UserCutsComponent`. mode: str If "exact", solves problem to optimality, keeping all optimality guarantees provided by the MIP solver. If "heuristic", uses machine learning more aggressively, and may return suboptimal solutions. solver: Callable[[], InternalSolver] A callable that constructs the internal solver. If None is provided, use GurobiPyomoSolver. use_lazy_cb: bool If true, use native solver callbacks for enforcing lazy constraints, instead of a simple loop. May not be supported by all solvers. solve_lp_first: bool If true, solve LP relaxation first, then solve original MILP. This option should be activated if the LP relaxation is not very expensive to solve and if it provides good hints for the integer solution. simulate_perfect: bool If true, each call to solve actually performs three actions: solve the original problem, train the ML models on the data that was just collected, and solve the problem again. This is useful for evaluating the theoretical performance of perfect ML models. """ def __init__( self, components: List[Component] = None, mode: str = "exact", solver: Callable[[], InternalSolver] = None, use_lazy_cb: bool = False, solve_lp_first: bool = True, simulate_perfect: bool = False, ): if solver is None: solver = GurobiPyomoSolver assert callable(solver), f"Callable expected. Found {solver.__class__} instead." self.components: Dict[str, Component] = {} self.internal_solver: Optional[InternalSolver] = None self.mode: str = mode self.simulate_perfect: bool = simulate_perfect self.solve_lp_first: bool = solve_lp_first self.solver_factory: Callable[[], InternalSolver] = solver self.tee = False self.use_lazy_cb: bool = use_lazy_cb if components is not None: for comp in components: self._add_component(comp) else: self._add_component(ObjectiveValueComponent()) self._add_component(PrimalSolutionComponent(mode=mode)) self._add_component(DynamicLazyConstraintsComponent()) self._add_component(UserCutsComponent()) assert self.mode in ["exact", "heuristic"] def _solve( self, instance: Union[Instance, str], model: Any = None, output_filename: Optional[str] = None, discard_output: bool = False, tee: bool = False, ) -> MIPSolveStats: # Load instance from file, if necessary filename = None fileformat = None file: Union[BinaryIO, gzip.GzipFile] if isinstance(instance, str): filename = instance logger.info("Reading: %s" % filename) if filename.endswith(".gz"): fileformat = "pickle-gz" with gzip.GzipFile(filename, "rb") as file: instance = pickle.load(cast(IO[bytes], file)) else: fileformat = "pickle" with open(filename, "rb") as file: instance = pickle.load(cast(IO[bytes], file)) assert isinstance(instance, Instance) # Generate model if model is None: with _RedirectOutput([]): model = instance.to_model() # Initialize training sample training_sample: TrainingSample = {} if not hasattr(instance, "training_data"): instance.training_data = [] instance.training_data += [training_sample] # Initialize internal solver self.tee = tee self.internal_solver = self.solver_factory() assert self.internal_solver is not None assert isinstance(self.internal_solver, InternalSolver) self.internal_solver.set_instance(instance, model) # Solve linear relaxation if self.solve_lp_first: logger.info("Solving LP relaxation...") lp_stats = self.internal_solver.solve_lp(tee=tee) training_sample["LP solution"] = self.internal_solver.get_solution() training_sample["LP value"] = lp_stats["Optimal value"] training_sample["LP log"] = lp_stats["Log"] else: training_sample["LP solution"] = self.internal_solver.get_empty_solution() training_sample["LP value"] = 0.0 # Before-solve callbacks logger.debug("Running before_solve callbacks...") for component in self.components.values(): component.before_solve(self, instance, model) # Define wrappers def iteration_cb_wrapper() -> bool: should_repeat = False assert isinstance(instance, Instance) for comp in self.components.values(): if comp.iteration_cb(self, instance, model): should_repeat = True return should_repeat def lazy_cb_wrapper( cb_solver: LearningSolver, cb_model: Any, ) -> None: assert isinstance(instance, Instance) for comp in self.components.values(): comp.lazy_cb(self, instance, model) lazy_cb = None if self.use_lazy_cb: lazy_cb = lazy_cb_wrapper # Solve MILP logger.info("Solving MILP...") stats = self.internal_solver.solve( tee=tee, iteration_cb=iteration_cb_wrapper, lazy_cb=lazy_cb, ) if "LP value" in training_sample.keys(): stats["LP value"] = training_sample["LP value"] # Read MIP solution and bounds training_sample["Lower bound"] = stats["Lower bound"] training_sample["Upper bound"] = stats["Upper bound"] training_sample["MIP log"] = stats["Log"] training_sample["Solution"] = self.internal_solver.get_solution() # After-solve callbacks logger.debug("Calling after_solve callbacks...") for component in self.components.values(): component.after_solve(self, instance, model, stats, training_sample) # Write to file, if necessary if not discard_output and filename is not None: if output_filename is None: output_filename = filename logger.info("Writing: %s" % output_filename) if fileformat == "pickle": with open(output_filename, "wb") as file: pickle.dump(instance, cast(IO[bytes], file)) else: with gzip.GzipFile(output_filename, "wb") as file: pickle.dump(instance, cast(IO[bytes], file)) return stats def solve( self, instance: Union[Instance, str], model: Any = None, output_filename: Optional[str] = None, discard_output: bool = False, tee: bool = False, ) -> MIPSolveStats: """ Solves the given instance. If trained machine-learning models are available, they will be used to accelerate the solution process. The argument `instance` may be either an Instance object or a filename pointing to a pickled Instance object. This method adds a new training sample to `instance.training_sample`. If a filename is provided, then the file is modified in-place. That is, the original file is overwritten. If `solver.solve_lp_first` is False, the properties lp_solution and lp_value will be set to dummy values. Parameters ---------- instance: Union[Instance, str] The instance to be solved, or a filename. model: Any The corresponding Pyomo model. If not provided, it will be created. output_filename: Optional[str] If instance is a filename and output_filename is provided, write the modified instance to this file, instead of replacing the original one. If output_filename is None (the default), modified the original file in-place. discard_output: bool If True, do not write the modified instances anywhere; simply discard them. Useful during benchmarking. tee: bool If true, prints solver log to screen. Returns ------- MIPSolveStats A dictionary of solver statistics containing at least the following keys: "Lower bound", "Upper bound", "Wallclock time", "Nodes", "Sense", "Log", "Warm start value" and "LP value". Additional components may generate additional keys. For example, ObjectiveValueComponent adds the keys "Predicted LB" and "Predicted UB". See the documentation of each component for more details. """ if self.simulate_perfect: if not isinstance(instance, str): raise Exception("Not implemented") with tempfile.NamedTemporaryFile(suffix=os.path.basename(instance)) as tmp: self._solve( instance=instance, model=model, output_filename=tmp.name, tee=tee, ) self.fit([tmp.name]) return self._solve( instance=instance, model=model, output_filename=output_filename, discard_output=discard_output, tee=tee, ) def parallel_solve( self, instances: Union[List[str], List[Instance]], n_jobs: int = 4, label: str = "Solve", output_filenames: Optional[List[str]] = None, discard_outputs: bool = False, ) -> List[MIPSolveStats]: """ Solves multiple instances in parallel. This method is equivalent to calling `solve` for each item on the list, but it processes multiple instances at the same time. Like `solve`, this method modifies each instance in place. Also like `solve`, a list of filenames may be provided. Parameters ---------- output_filenames: Optional[List[str]] If instances are file names and output_filenames is provided, write the modified instances to these files, instead of replacing the original files. If output_filenames is None, modifies the instances in-place. discard_outputs: bool If True, do not write the modified instances anywhere; simply discard them instead. Useful during benchmarking. label: str Label to show in the progress bar. instances: Union[List[str], List[Instance]] The instances to be solved n_jobs: int Number of instances to solve in parallel at a time. Returns ------- List[MIPSolveStats] List of solver statistics, with one entry for each provided instance. The list is the same you would obtain by calling `[solver.solve(p) for p in instances]` """ self.internal_solver = None self._silence_miplearn_logger() _GLOBAL[0].solver = self _GLOBAL[0].output_filenames = output_filenames _GLOBAL[0].instances = instances _GLOBAL[0].discard_outputs = discard_outputs results = p_map( _parallel_solve, list(range(len(instances))), num_cpus=n_jobs, desc=label, ) stats = [] for (idx, (s, instance)) in enumerate(results): stats.append(s) instances[idx] = instance self._restore_miplearn_logger() return stats def fit(self, training_instances: Union[List[str], List[Instance]]) -> None: if len(training_instances) == 0: return for component in self.components.values(): component.fit(training_instances) def _add_component(self, component: Component) -> None: name = component.__class__.__name__ self.components[name] = component def _silence_miplearn_logger(self) -> None: miplearn_logger = logging.getLogger("miplearn") self.prev_log_level = miplearn_logger.getEffectiveLevel() miplearn_logger.setLevel(logging.WARNING) def _restore_miplearn_logger(self) -> None: miplearn_logger = logging.getLogger("miplearn") miplearn_logger.setLevel(self.prev_log_level) def __getstate__(self) -> Dict: self.internal_solver = None return self.__dict__Methods
def fit(self, training_instances)-
Expand source code
def fit(self, training_instances: Union[List[str], List[Instance]]) -> None: if len(training_instances) == 0: return for component in self.components.values(): component.fit(training_instances) def parallel_solve(self, instances, n_jobs=4, label='Solve', output_filenames=None, discard_outputs=False)-
Solves multiple instances in parallel.
This method is equivalent to calling
solvefor each item on the list, but it processes multiple instances at the same time. Likesolve, this method modifies each instance in place. Also likesolve, a list of filenames may be provided.Parameters
output_filenames:Optional[List[str]]- If instances are file names and output_filenames is provided, write the modified instances to these files, instead of replacing the original files. If output_filenames is None, modifies the instances in-place.
discard_outputs:bool- If True, do not write the modified instances anywhere; simply discard them instead. Useful during benchmarking.
label:str- Label to show in the progress bar.
instances:Union[List[str],List[Instance]]- The instances to be solved
n_jobs:int- Number of instances to solve in parallel at a time.
Returns
List[MIPSolveStats]- List of solver statistics, with one entry for each provided instance.
The list is the same you would obtain by calling
[solver.solve(p) for p in instances]
Expand source code
def parallel_solve( self, instances: Union[List[str], List[Instance]], n_jobs: int = 4, label: str = "Solve", output_filenames: Optional[List[str]] = None, discard_outputs: bool = False, ) -> List[MIPSolveStats]: """ Solves multiple instances in parallel. This method is equivalent to calling `solve` for each item on the list, but it processes multiple instances at the same time. Like `solve`, this method modifies each instance in place. Also like `solve`, a list of filenames may be provided. Parameters ---------- output_filenames: Optional[List[str]] If instances are file names and output_filenames is provided, write the modified instances to these files, instead of replacing the original files. If output_filenames is None, modifies the instances in-place. discard_outputs: bool If True, do not write the modified instances anywhere; simply discard them instead. Useful during benchmarking. label: str Label to show in the progress bar. instances: Union[List[str], List[Instance]] The instances to be solved n_jobs: int Number of instances to solve in parallel at a time. Returns ------- List[MIPSolveStats] List of solver statistics, with one entry for each provided instance. The list is the same you would obtain by calling `[solver.solve(p) for p in instances]` """ self.internal_solver = None self._silence_miplearn_logger() _GLOBAL[0].solver = self _GLOBAL[0].output_filenames = output_filenames _GLOBAL[0].instances = instances _GLOBAL[0].discard_outputs = discard_outputs results = p_map( _parallel_solve, list(range(len(instances))), num_cpus=n_jobs, desc=label, ) stats = [] for (idx, (s, instance)) in enumerate(results): stats.append(s) instances[idx] = instance self._restore_miplearn_logger() return stats def solve(self, instance, model=None, output_filename=None, discard_output=False, tee=False)-
Solves the given instance. If trained machine-learning models are available, they will be used to accelerate the solution process.
The argument
instancemay be either an Instance object or a filename pointing to a pickled Instance object.This method adds a new training sample to
instance.training_sample. If a filename is provided, then the file is modified in-place. That is, the original file is overwritten.If
solver.solve_lp_firstis False, the properties lp_solution and lp_value will be set to dummy values.Parameters
instance:Union[Instance,str]- The instance to be solved, or a filename.
model:Any- The corresponding Pyomo model. If not provided, it will be created.
output_filename:Optional[str]- If instance is a filename and output_filename is provided, write the modified instance to this file, instead of replacing the original one. If output_filename is None (the default), modified the original file in-place.
discard_output:bool- If True, do not write the modified instances anywhere; simply discard them. Useful during benchmarking.
tee:bool- If true, prints solver log to screen.
Returns
MIPSolveStats-
A dictionary of solver statistics containing at least the following keys: "Lower bound", "Upper bound", "Wallclock time", "Nodes", "Sense", "Log", "Warm start value" and "LP value".
Additional components may generate additional keys. For example, ObjectiveValueComponent adds the keys "Predicted LB" and "Predicted UB". See the documentation of each component for more details.
Expand source code
def solve( self, instance: Union[Instance, str], model: Any = None, output_filename: Optional[str] = None, discard_output: bool = False, tee: bool = False, ) -> MIPSolveStats: """ Solves the given instance. If trained machine-learning models are available, they will be used to accelerate the solution process. The argument `instance` may be either an Instance object or a filename pointing to a pickled Instance object. This method adds a new training sample to `instance.training_sample`. If a filename is provided, then the file is modified in-place. That is, the original file is overwritten. If `solver.solve_lp_first` is False, the properties lp_solution and lp_value will be set to dummy values. Parameters ---------- instance: Union[Instance, str] The instance to be solved, or a filename. model: Any The corresponding Pyomo model. If not provided, it will be created. output_filename: Optional[str] If instance is a filename and output_filename is provided, write the modified instance to this file, instead of replacing the original one. If output_filename is None (the default), modified the original file in-place. discard_output: bool If True, do not write the modified instances anywhere; simply discard them. Useful during benchmarking. tee: bool If true, prints solver log to screen. Returns ------- MIPSolveStats A dictionary of solver statistics containing at least the following keys: "Lower bound", "Upper bound", "Wallclock time", "Nodes", "Sense", "Log", "Warm start value" and "LP value". Additional components may generate additional keys. For example, ObjectiveValueComponent adds the keys "Predicted LB" and "Predicted UB". See the documentation of each component for more details. """ if self.simulate_perfect: if not isinstance(instance, str): raise Exception("Not implemented") with tempfile.NamedTemporaryFile(suffix=os.path.basename(instance)) as tmp: self._solve( instance=instance, model=model, output_filename=tmp.name, tee=tee, ) self.fit([tmp.name]) return self._solve( instance=instance, model=model, output_filename=output_filename, discard_output=discard_output, tee=tee, )