97 lines
3.7 KiB
C++
97 lines
3.7 KiB
C++
// Copyright 2010-2018 Google LLC
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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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#include "ortools/sat/cp_model_objective.h"
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#include "ortools/sat/cp_model_utils.h"
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namespace operations_research {
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namespace sat {
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void EncodeObjectiveAsSingleVariable(CpModelProto* cp_model) {
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if (!cp_model->has_objective()) return;
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if (cp_model->objective().vars_size() == 1) {
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// Canonicalize the objective to make it easier on us by always making the
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// coefficient equal to 1.0.
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const int old_ref = cp_model->objective().vars(0);
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const int64 old_coeff = cp_model->objective().coeffs(0);
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const double muliplier = static_cast<double>(std::abs(old_coeff));
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if (old_coeff < 0) {
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cp_model->mutable_objective()->set_vars(0, NegatedRef(old_ref));
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}
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if (muliplier != 1.0) {
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// TODO(user): deal with this case.
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CHECK(cp_model->objective().domain().empty());
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double old_factor = cp_model->objective().scaling_factor();
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if (old_factor == 0.0) old_factor = 1.0;
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const double old_offset = cp_model->objective().offset();
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cp_model->mutable_objective()->set_scaling_factor(old_factor * muliplier);
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cp_model->mutable_objective()->set_offset(old_offset / muliplier);
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}
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cp_model->mutable_objective()->set_coeffs(0, 1.0);
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return;
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}
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// Compute trivial bounds on the objective, this is needed otherwise the
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// overflow checker might not be happy with the new constraint we are about
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// to create. Note that the model validator should make sure that there is no
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// overflow in the computation below.
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int64 min_obj = 0;
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int64 max_obj = 0;
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for (int i = 0; i < cp_model->objective().vars_size(); ++i) {
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const int ref = cp_model->objective().vars(i);
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const int var = PositiveRef(ref);
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const int64 coeff =
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cp_model->objective().coeffs(i) * (RefIsPositive(ref) ? 1 : -1);
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const int64 value1 = cp_model->variables(var).domain(0) * coeff;
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const int64 value2 = cp_model->variables(var).domain(
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cp_model->variables(var).domain_size() - 1) *
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coeff;
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min_obj += std::min(value1, value2);
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max_obj += std::max(value1, value2);
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}
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// Create the new objective var.
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const int obj_ref = cp_model->variables_size();
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{
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IntegerVariableProto* obj = cp_model->add_variables();
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Domain obj_domain(min_obj, max_obj);
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if (!cp_model->objective().domain().empty()) {
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obj_domain = obj_domain.IntersectionWith(
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ReadDomainFromProto(cp_model->objective()));
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}
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FillDomainInProto(obj_domain, obj);
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}
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// Add the linear constraint.
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LinearConstraintProto* ct = cp_model->add_constraints()->mutable_linear();
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ct->add_domain(0);
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ct->add_domain(0);
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*(ct->mutable_vars()) = cp_model->objective().vars();
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*(ct->mutable_coeffs()) = cp_model->objective().coeffs();
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ct->add_vars(obj_ref);
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ct->add_coeffs(-1);
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// Update the objective.
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cp_model->mutable_objective()->clear_vars();
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cp_model->mutable_objective()->clear_coeffs();
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cp_model->mutable_objective()->add_vars(obj_ref);
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cp_model->mutable_objective()->add_coeffs(1);
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cp_model->mutable_objective()->clear_domain();
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}
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} // namespace sat
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} // namespace operations_research
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