141 lines
4.1 KiB
Python
141 lines
4.1 KiB
Python
# Copyright 2010-2014 Google
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Examples showing how to use the python API of the constraint solver.
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See python/constraint_solver.swig.
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This example file can also be used as a unit test.
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"""
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from ortools.constraint_solver import pywrapcp
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class OneVarLns(pywrapcp.PyLns):
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"""One Var LNS."""
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def __init__(self, variables):
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pywrapcp.PyLns.__init__(self, variables)
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self.__index = 0
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def InitFragments(self):
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self.__index = 0
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def NextFragment(self):
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if self.__index < self.Size():
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self.__index += 1
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return [self.__index - 1]
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else:
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return []
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class MoveOneVar(pywrapcp.IntVarLocalSearchOperator):
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"""Move one var up or down."""
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def __init__(self, variables):
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pywrapcp.IntVarLocalSearchOperator.__init__(self, variables)
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self.__index = 0
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self.__up = False
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def OneNeighbor(self):
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current_value = self.OldValue(self.__index)
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if self.__up:
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self.SetValue(self.__index, current_value + 1)
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self.__index = (self.__index + 1) % self.Size()
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else:
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self.SetValue(self.__index, current_value - 1)
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self.__up = not self.__up
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return True
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def OnStart(self):
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pass
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def IsIncremental(self):
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return False
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class SumFilter(pywrapcp.IntVarLocalSearchFilter):
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"""Filter to speed up LS computation."""
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def __init__(self, variables):
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pywrapcp.IntVarLocalSearchFilter.__init__(self, variables)
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self.__sum = 0
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def OnSynchronize(self, delta):
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self.__sum = sum(self.Value(index) for index in range(self.Size()))
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def Accept(self, delta, _):
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solution_delta = delta.IntVarContainer()
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solution_delta_size = solution_delta.Size()
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for i in range(solution_delta_size):
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if not solution_delta.Element(i).Activated():
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return True
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new_sum = self.__sum
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for i in range(solution_delta_size):
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element = solution_delta.Element(i)
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int_var = element.Var()
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touched_var_index = self.IndexFromVar(int_var)
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old_value = self.Value(touched_var_index)
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new_value = element.Value()
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new_sum += new_value - old_value
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return new_sum < self.__sum
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def IsIncremental(self):
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return False
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def Solve(example_index):
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"""Run one of 3 simple examples of local search."""
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solver = pywrapcp.Solver('Solve')
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variables = [solver.IntVar(0, 4) for _ in range(4)]
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sum_var = solver.Sum(variables)
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obj = solver.Minimize(sum_var, 1)
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db = solver.Phase(variables, solver.CHOOSE_FIRST_UNBOUND,
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solver.ASSIGN_MAX_VALUE)
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ls = None
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if example_index == 0: # LNS
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print 'Large Neighborhood Search'
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one_var_lns = OneVarLns(variables)
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ls_params = solver.LocalSearchPhaseParameters(one_var_lns, db)
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ls = solver.LocalSearchPhase(variables, db, ls_params)
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elif example_index == 1: # LS
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print 'Local Search'
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move_one_var = MoveOneVar(variables)
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ls_params = solver.LocalSearchPhaseParameters(move_one_var, db)
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ls = solver.LocalSearchPhase(variables, db, ls_params)
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else:
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print 'Local Search with Filter'
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move_one_var = MoveOneVar(variables)
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sum_filter = SumFilter(variables)
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ls_params = solver.LocalSearchPhaseParameters(move_one_var, db, None,
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[sum_filter])
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ls = solver.LocalSearchPhase(variables, db, ls_params)
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collector = solver.LastSolutionCollector()
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collector.Add(variables)
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collector.AddObjective(sum_var)
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log = solver.SearchLog(1000, obj)
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solver.Solve(ls, [collector, obj, log])
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print 'Objective value = %d' % collector.ObjectiveValue(0)
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def main(_):
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Solve(0)
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Solve(1)
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Solve(2)
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if __name__ == '__main__':
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main()
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