# Copyright (c) 2022 AIRBUS and its affiliates.
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
import random
from typing import Any, Iterable, Optional
from minizinc import Instance
from discrete_optimization.generic_tools.cp_tools import CPSolver
from discrete_optimization.generic_tools.hyperparameters.hyperparameter import (
FloatHyperparameter,
)
from discrete_optimization.generic_tools.lns_cp import ConstraintHandler
from discrete_optimization.knapsack.knapsack_model import (
KnapsackModel,
KnapsackSolution,
)
from discrete_optimization.knapsack.solvers.cp_solvers import CPKnapsackMZN2
from discrete_optimization.knapsack.solvers.greedy_solvers import ResultStorage
[docs]
class ConstraintHandlerKnapsack(ConstraintHandler):
hyperparameters = [
FloatHyperparameter(name="fraction_to_fix", default=0.9, low=0.0, high=1.0),
]
def __init__(self, problem: KnapsackModel, fraction_to_fix: float = 0.9):
self.problem = problem
self.fraction_to_fix = fraction_to_fix
self.iter = 0
[docs]
def adding_constraint_from_results_store(
self,
cp_solver: CPSolver,
child_instance: Instance,
result_storage: ResultStorage,
last_result_store: Optional[ResultStorage] = None,
) -> Iterable[Any]:
if not isinstance(cp_solver, CPKnapsackMZN2):
raise ValueError("cp_solver must a CPKnapsackMZN2 for this constraint.")
subpart_item = set(
random.sample(
range(self.problem.nb_items),
int(self.fraction_to_fix * self.problem.nb_items),
)
)
current_solution = result_storage.get_best_solution()
if current_solution is None:
raise ValueError(
"result_storage.get_best_solution() " "should not be None."
)
if not isinstance(current_solution, KnapsackSolution):
raise ValueError(
"result_storage.get_best_solution() " "should be a KnapsackSolution."
)
list_strings = []
for item in subpart_item:
list_strings += [
"constraint taken["
+ str(item + 1)
+ "] == "
+ str(current_solution.list_taken[item])
+ ";\n"
]
child_instance.add_string(list_strings[-1])
return list_strings
[docs]
def remove_constraints_from_previous_iteration(
self,
cp_solver: CPSolver,
child_instance: Instance,
previous_constraints: Iterable[Any],
) -> None:
if not isinstance(cp_solver, CPKnapsackMZN2):
raise ValueError("cp_solver must a CPKnapsackMZN2 for this constraint.")
pass