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gurobi_proto_solver.cc
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gurobi_proto_solver.cc
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// Copyright 2010-2021 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "ortools/linear_solver/gurobi_proto_solver.h"
#include <limits>
#include <memory>
#include <numeric>
#include <string>
#include <vector>
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include "absl/strings/str_join.h"
#include "absl/strings/str_split.h"
#include "absl/types/optional.h"
#include "ortools/base/cleanup.h"
#include "ortools/base/status_macros.h"
#include "ortools/base/timer.h"
#include "ortools/gurobi/environment.h"
#include "ortools/linear_solver/linear_solver.h"
#include "ortools/linear_solver/linear_solver.pb.h"
#include "ortools/linear_solver/model_validator.h"
#include "ortools/util/lazy_mutable_copy.h"
namespace operations_research {
namespace {
constexpr int GRB_OK = 0;
inline absl::Status GurobiCodeToUtilStatus(int error_code,
const char* source_file,
int source_line,
const char* statement,
GRBenv* const env) {
if (error_code == GRB_OK) return absl::OkStatus();
return absl::InvalidArgumentError(absl::StrFormat(
"Gurobi error code %d (file '%s', line %d) on '%s': %s", error_code,
source_file, source_line, statement, GRBgeterrormsg(env)));
}
int AddIndicatorConstraint(const MPGeneralConstraintProto& gen_cst,
GRBmodel* gurobi_model,
std::vector<int>* tmp_variables,
std::vector<double>* tmp_coefficients) {
CHECK(gurobi_model != nullptr);
CHECK(tmp_variables != nullptr);
CHECK(tmp_coefficients != nullptr);
const auto& ind_cst = gen_cst.indicator_constraint();
MPConstraintProto cst = ind_cst.constraint();
if (cst.lower_bound() > -std::numeric_limits<double>::infinity()) {
int status = GRBaddgenconstrIndicator(
gurobi_model, gen_cst.name().c_str(), ind_cst.var_index(),
ind_cst.var_value(), cst.var_index_size(),
cst.mutable_var_index()->mutable_data(),
cst.mutable_coefficient()->mutable_data(),
cst.upper_bound() == cst.lower_bound() ? GRB_EQUAL : GRB_GREATER_EQUAL,
cst.lower_bound());
if (status != GRB_OK) return status;
}
if (cst.upper_bound() < std::numeric_limits<double>::infinity() &&
cst.lower_bound() != cst.upper_bound()) {
return GRBaddgenconstrIndicator(gurobi_model, gen_cst.name().c_str(),
ind_cst.var_index(), ind_cst.var_value(),
cst.var_index_size(),
cst.mutable_var_index()->mutable_data(),
cst.mutable_coefficient()->mutable_data(),
GRB_LESS_EQUAL, cst.upper_bound());
}
return GRB_OK;
}
int AddSosConstraint(const MPSosConstraint& sos_cst, GRBmodel* gurobi_model,
std::vector<int>* tmp_variables,
std::vector<double>* tmp_weights) {
CHECK(gurobi_model != nullptr);
CHECK(tmp_variables != nullptr);
CHECK(tmp_weights != nullptr);
tmp_variables->resize(sos_cst.var_index_size(), 0);
for (int v = 0; v < sos_cst.var_index_size(); ++v) {
(*tmp_variables)[v] = sos_cst.var_index(v);
}
tmp_weights->resize(sos_cst.var_index_size(), 0);
if (sos_cst.weight_size() == sos_cst.var_index_size()) {
for (int w = 0; w < sos_cst.weight_size(); ++w) {
(*tmp_weights)[w] = sos_cst.weight(w);
}
} else {
DCHECK_EQ(sos_cst.weight_size(), 0);
// Gurobi requires variable weights in their SOS constraints.
std::iota(tmp_weights->begin(), tmp_weights->end(), 1);
}
std::vector<int> types = {sos_cst.type() == MPSosConstraint::SOS1_DEFAULT
? GRB_SOS_TYPE1
: GRB_SOS_TYPE2};
std::vector<int> begins = {0};
return GRBaddsos(gurobi_model, /*numsos=*/1,
/*nummembers=*/sos_cst.var_index_size(),
/*types=*/types.data(),
/*beg=*/begins.data(), /*ind=*/tmp_variables->data(),
/*weight*/ tmp_weights->data());
}
int AddQuadraticConstraint(const MPGeneralConstraintProto& gen_cst,
GRBmodel* gurobi_model) {
CHECK(gurobi_model != nullptr);
constexpr double kInfinity = std::numeric_limits<double>::infinity();
CHECK(gen_cst.has_quadratic_constraint());
const MPQuadraticConstraint& quad_cst = gen_cst.quadratic_constraint();
auto addqconstr = [](GRBmodel* gurobi_model, MPQuadraticConstraint quad_cst,
char sense, double rhs, const std::string& name) {
return GRBaddqconstr(
gurobi_model,
/*numlnz=*/quad_cst.var_index_size(),
/*lind=*/quad_cst.mutable_var_index()->mutable_data(),
/*lval=*/quad_cst.mutable_coefficient()->mutable_data(),
/*numqnz=*/quad_cst.qvar1_index_size(),
/*qrow=*/quad_cst.mutable_qvar1_index()->mutable_data(),
/*qcol=*/quad_cst.mutable_qvar2_index()->mutable_data(),
/*qval=*/quad_cst.mutable_qcoefficient()->mutable_data(),
/*sense=*/sense,
/*rhs=*/rhs,
/*QCname=*/name.c_str());
};
if (quad_cst.has_lower_bound() && quad_cst.lower_bound() > -kInfinity) {
const int grb_status =
addqconstr(gurobi_model, gen_cst.quadratic_constraint(),
GRB_GREATER_EQUAL, quad_cst.lower_bound(),
gen_cst.has_name() ? gen_cst.name() + "_lb" : "");
if (grb_status != GRB_OK) return grb_status;
}
if (quad_cst.has_upper_bound() && quad_cst.upper_bound() < kInfinity) {
const int grb_status =
addqconstr(gurobi_model, gen_cst.quadratic_constraint(), GRB_LESS_EQUAL,
quad_cst.upper_bound(),
gen_cst.has_name() ? gen_cst.name() + "_ub" : "");
if (grb_status != GRB_OK) return grb_status;
}
return GRB_OK;
}
int AddAndConstraint(const MPGeneralConstraintProto& gen_cst,
GRBmodel* gurobi_model, std::vector<int>* tmp_variables) {
CHECK(gurobi_model != nullptr);
CHECK(tmp_variables != nullptr);
auto and_cst = gen_cst.and_constraint();
return GRBaddgenconstrAnd(
gurobi_model,
/*name=*/gen_cst.name().c_str(),
/*resvar=*/and_cst.resultant_var_index(),
/*nvars=*/and_cst.var_index_size(),
/*vars=*/and_cst.mutable_var_index()->mutable_data());
}
int AddOrConstraint(const MPGeneralConstraintProto& gen_cst,
GRBmodel* gurobi_model, std::vector<int>* tmp_variables) {
CHECK(gurobi_model != nullptr);
CHECK(tmp_variables != nullptr);
auto or_cst = gen_cst.or_constraint();
return GRBaddgenconstrOr(gurobi_model,
/*name=*/gen_cst.name().c_str(),
/*resvar=*/or_cst.resultant_var_index(),
/*nvars=*/or_cst.var_index_size(),
/*vars=*/or_cst.mutable_var_index()->mutable_data());
}
int AddMinConstraint(const MPGeneralConstraintProto& gen_cst,
GRBmodel* gurobi_model, std::vector<int>* tmp_variables) {
CHECK(gurobi_model != nullptr);
CHECK(tmp_variables != nullptr);
auto min_cst = gen_cst.min_constraint();
return GRBaddgenconstrMin(
gurobi_model,
/*name=*/gen_cst.name().c_str(),
/*resvar=*/min_cst.resultant_var_index(),
/*nvars=*/min_cst.var_index_size(),
/*vars=*/min_cst.mutable_var_index()->mutable_data(),
/*constant=*/min_cst.has_constant()
? min_cst.constant()
: std::numeric_limits<double>::infinity());
}
int AddMaxConstraint(const MPGeneralConstraintProto& gen_cst,
GRBmodel* gurobi_model, std::vector<int>* tmp_variables) {
CHECK(gurobi_model != nullptr);
CHECK(tmp_variables != nullptr);
auto max_cst = gen_cst.max_constraint();
return GRBaddgenconstrMax(
gurobi_model,
/*name=*/gen_cst.name().c_str(),
/*resvar=*/max_cst.resultant_var_index(),
/*nvars=*/max_cst.var_index_size(),
/*vars=*/max_cst.mutable_var_index()->mutable_data(),
/*constant=*/max_cst.has_constant()
? max_cst.constant()
: -std::numeric_limits<double>::infinity());
}
} // namespace
absl::Status SetSolverSpecificParameters(const std::string& parameters,
GRBenv* gurobi) {
if (parameters.empty()) return absl::OkStatus();
std::vector<std::string> error_messages;
for (absl::string_view line : absl::StrSplit(parameters, '\n')) {
// Comment tokens end at the next new-line, or the end of the string.
// The first character must be '#'
if (line[0] == '#') continue;
for (absl::string_view token :
absl::StrSplit(line, ',', absl::SkipWhitespace())) {
if (token.empty()) continue;
std::vector<std::string> key_value =
absl::StrSplit(token, absl::ByAnyChar(" ="), absl::SkipWhitespace());
// If one parameter fails, we keep processing the list of parameters.
if (key_value.size() != 2) {
const std::string current_message =
absl::StrCat("Cannot parse parameter '", token,
"'. Expected format is 'ParameterName value' or "
"'ParameterName=value'");
error_messages.push_back(current_message);
continue;
}
const int gurobi_code =
GRBsetparam(gurobi, key_value[0].c_str(), key_value[1].c_str());
if (gurobi_code != GRB_OK) {
const std::string current_message = absl::StrCat(
"Error setting parameter '", key_value[0], "' to value '",
key_value[1], "': ", GRBgeterrormsg(gurobi));
error_messages.push_back(current_message);
continue;
}
VLOG(2) << absl::StrCat("Set parameter '", key_value[0], "' to value '",
key_value[1]);
}
}
if (error_messages.empty()) return absl::OkStatus();
return absl::InvalidArgumentError(absl::StrJoin(error_messages, "\n"));
}
absl::StatusOr<MPSolutionResponse> GurobiSolveProto(
const MPModelRequest& request, GRBenv* gurobi_env) {
MPSolutionResponse response;
const absl::optional<LazyMutableCopy<MPModelProto>> optional_model =
ExtractValidMPModelOrPopulateResponseStatus(request, &response);
if (!optional_model) return response;
const MPModelProto& model = optional_model->get();
// We set `gurobi_env` to point to a new environment if no existing one is
// provided. We must make sure that we free this environment when we exit this
// function.
bool gurobi_env_was_created = false;
auto gurobi_env_deleter = absl::MakeCleanup([&]() {
if (gurobi_env_was_created && gurobi_env != nullptr) {
GRBfreeenv(gurobi_env);
}
});
if (gurobi_env == nullptr) {
ASSIGN_OR_RETURN(gurobi_env, GetGurobiEnv());
gurobi_env_was_created = true;
}
GRBmodel* gurobi_model = nullptr;
auto gurobi_model_deleter = absl::MakeCleanup([&]() {
const int error_code = GRBfreemodel(gurobi_model);
LOG_IF(DFATAL, error_code != GRB_OK)
<< "GRBfreemodel failed with error " << error_code << ": "
<< GRBgeterrormsg(gurobi_env);
});
// `gurobi_env` references ther GRBenv argument.
#define RETURN_IF_GUROBI_ERROR(x) \
RETURN_IF_ERROR( \
GurobiCodeToUtilStatus(x, __FILE__, __LINE__, #x, gurobi_env));
RETURN_IF_GUROBI_ERROR(GRBnewmodel(gurobi_env, &gurobi_model,
model.name().c_str(),
/*numvars=*/0,
/*obj=*/nullptr,
/*lb=*/nullptr,
/*ub=*/nullptr,
/*vtype=*/nullptr,
/*varnames=*/nullptr));
GRBenv* const model_env = GRBgetenv(gurobi_model);
if (request.has_solver_specific_parameters()) {
const auto parameters_status = SetSolverSpecificParameters(
request.solver_specific_parameters(), model_env);
if (!parameters_status.ok()) {
response.set_status(MPSOLVER_MODEL_INVALID_SOLVER_PARAMETERS);
response.set_status_str(
std::string(parameters_status.message())); // NOLINT
return response;
}
}
if (request.solver_time_limit_seconds() > 0) {
RETURN_IF_GUROBI_ERROR(GRBsetdblparam(model_env, GRB_DBL_PAR_TIMELIMIT,
request.solver_time_limit_seconds()));
}
RETURN_IF_GUROBI_ERROR(
GRBsetintparam(model_env, GRB_INT_PAR_OUTPUTFLAG,
request.enable_internal_solver_output()));
const int variable_size = model.variable_size();
bool has_integer_variables = false;
{
std::vector<double> obj_coeffs(variable_size, 0);
std::vector<double> lb(variable_size);
std::vector<double> ub(variable_size);
std::vector<char> ctype(variable_size);
std::vector<const char*> varnames(variable_size);
for (int v = 0; v < variable_size; ++v) {
const MPVariableProto& variable = model.variable(v);
obj_coeffs[v] = variable.objective_coefficient();
lb[v] = variable.lower_bound();
ub[v] = variable.upper_bound();
ctype[v] = variable.is_integer() && SolverTypeIsMip(request.solver_type())
? GRB_INTEGER
: GRB_CONTINUOUS;
if (variable.is_integer()) has_integer_variables = true;
if (!variable.name().empty()) varnames[v] = variable.name().c_str();
}
RETURN_IF_GUROBI_ERROR(
GRBaddvars(gurobi_model, variable_size, 0, nullptr, nullptr, nullptr,
/*obj=*/obj_coeffs.data(),
/*lb=*/lb.data(), /*ub=*/ub.data(), /*vtype=*/ctype.data(),
/*varnames=*/const_cast<char**>(varnames.data())));
// Set solution hints if any.
for (int i = 0; i < model.solution_hint().var_index_size(); ++i) {
RETURN_IF_GUROBI_ERROR(GRBsetdblattrelement(
gurobi_model, GRB_DBL_ATTR_START, model.solution_hint().var_index(i),
model.solution_hint().var_value(i)));
}
}
{
std::vector<int> ct_variables;
std::vector<double> ct_coefficients;
for (int c = 0; c < model.constraint_size(); ++c) {
const MPConstraintProto& constraint = model.constraint(c);
const int size = constraint.var_index_size();
ct_variables.resize(size, 0);
ct_coefficients.resize(size, 0);
for (int i = 0; i < size; ++i) {
ct_variables[i] = constraint.var_index(i);
ct_coefficients[i] = constraint.coefficient(i);
}
// Using GRBaddrangeconstr for constraints that don't require it adds
// a slack which is not always removed by presolve.
if (constraint.lower_bound() == constraint.upper_bound()) {
RETURN_IF_GUROBI_ERROR(GRBaddconstr(
gurobi_model, /*numnz=*/size, /*cind=*/ct_variables.data(),
/*cval=*/ct_coefficients.data(),
/*sense=*/GRB_EQUAL, /*rhs=*/constraint.lower_bound(),
/*constrname=*/constraint.name().c_str()));
} else if (constraint.lower_bound() ==
-std::numeric_limits<double>::infinity()) {
RETURN_IF_GUROBI_ERROR(GRBaddconstr(
gurobi_model, /*numnz=*/size, /*cind=*/ct_variables.data(),
/*cval=*/ct_coefficients.data(),
/*sense=*/GRB_LESS_EQUAL, /*rhs=*/constraint.upper_bound(),
/*constrname=*/constraint.name().c_str()));
} else if (constraint.upper_bound() ==
std::numeric_limits<double>::infinity()) {
RETURN_IF_GUROBI_ERROR(GRBaddconstr(
gurobi_model, /*numnz=*/size, /*cind=*/ct_variables.data(),
/*cval=*/ct_coefficients.data(),
/*sense=*/GRB_GREATER_EQUAL, /*rhs=*/constraint.lower_bound(),
/*constrname=*/constraint.name().c_str()));
} else {
RETURN_IF_GUROBI_ERROR(GRBaddrangeconstr(
gurobi_model, /*numnz=*/size, /*cind=*/ct_variables.data(),
/*cval=*/ct_coefficients.data(),
/*lower=*/constraint.lower_bound(),
/*upper=*/constraint.upper_bound(),
/*constrname=*/constraint.name().c_str()));
}
}
for (const auto& gen_cst : model.general_constraint()) {
switch (gen_cst.general_constraint_case()) {
case MPGeneralConstraintProto::kIndicatorConstraint: {
RETURN_IF_GUROBI_ERROR(AddIndicatorConstraint(
gen_cst, gurobi_model, &ct_variables, &ct_coefficients));
break;
}
case MPGeneralConstraintProto::kSosConstraint: {
RETURN_IF_GUROBI_ERROR(AddSosConstraint(gen_cst.sos_constraint(),
gurobi_model, &ct_variables,
&ct_coefficients));
break;
}
case MPGeneralConstraintProto::kQuadraticConstraint: {
RETURN_IF_GUROBI_ERROR(AddQuadraticConstraint(gen_cst, gurobi_model));
break;
}
case MPGeneralConstraintProto::kAbsConstraint: {
RETURN_IF_GUROBI_ERROR(GRBaddgenconstrAbs(
gurobi_model,
/*name=*/gen_cst.name().c_str(),
/*resvar=*/gen_cst.abs_constraint().resultant_var_index(),
/*argvar=*/gen_cst.abs_constraint().var_index()));
break;
}
case MPGeneralConstraintProto::kAndConstraint: {
RETURN_IF_GUROBI_ERROR(
AddAndConstraint(gen_cst, gurobi_model, &ct_variables));
break;
}
case MPGeneralConstraintProto::kOrConstraint: {
RETURN_IF_GUROBI_ERROR(
AddOrConstraint(gen_cst, gurobi_model, &ct_variables));
break;
}
case MPGeneralConstraintProto::kMinConstraint: {
RETURN_IF_GUROBI_ERROR(
AddMinConstraint(gen_cst, gurobi_model, &ct_variables));
break;
}
case MPGeneralConstraintProto::kMaxConstraint: {
RETURN_IF_GUROBI_ERROR(
AddMaxConstraint(gen_cst, gurobi_model, &ct_variables));
break;
}
default:
return absl::UnimplementedError(
absl::StrFormat("General constraints of type %i not supported.",
gen_cst.general_constraint_case()));
}
}
}
RETURN_IF_GUROBI_ERROR(GRBsetintattr(gurobi_model, GRB_INT_ATTR_MODELSENSE,
model.maximize() ? -1 : 1));
RETURN_IF_GUROBI_ERROR(GRBsetdblattr(gurobi_model, GRB_DBL_ATTR_OBJCON,
model.objective_offset()));
if (model.has_quadratic_objective()) {
MPQuadraticObjective qobj = model.quadratic_objective();
if (qobj.coefficient_size() > 0) {
RETURN_IF_GUROBI_ERROR(
GRBaddqpterms(gurobi_model, /*numqnz=*/qobj.coefficient_size(),
/*qrow=*/qobj.mutable_qvar1_index()->mutable_data(),
/*qcol=*/qobj.mutable_qvar2_index()->mutable_data(),
/*qval=*/qobj.mutable_coefficient()->mutable_data()));
}
}
RETURN_IF_GUROBI_ERROR(GRBupdatemodel(gurobi_model));
const absl::Time time_before = absl::Now();
UserTimer user_timer;
user_timer.Start();
RETURN_IF_GUROBI_ERROR(GRBoptimize(gurobi_model));
const absl::Duration solving_duration = absl::Now() - time_before;
user_timer.Stop();
VLOG(1) << "Finished solving in GurobiSolveProto(), walltime = "
<< solving_duration << ", usertime = " << user_timer.GetDuration();
response.mutable_solve_info()->set_solve_wall_time_seconds(
absl::ToDoubleSeconds(solving_duration));
response.mutable_solve_info()->set_solve_user_time_seconds(
absl::ToDoubleSeconds(user_timer.GetDuration()));
int optimization_status = 0;
RETURN_IF_GUROBI_ERROR(
GRBgetintattr(gurobi_model, GRB_INT_ATTR_STATUS, &optimization_status));
int solution_count = 0;
RETURN_IF_GUROBI_ERROR(
GRBgetintattr(gurobi_model, GRB_INT_ATTR_SOLCOUNT, &solution_count));
switch (optimization_status) {
case GRB_OPTIMAL:
response.set_status(MPSOLVER_OPTIMAL);
break;
case GRB_INF_OR_UNBD:
DLOG(INFO) << "Gurobi solve returned GRB_INF_OR_UNBD, which we treat as "
"INFEASIBLE even though it may mean UNBOUNDED.";
response.set_status_str(
"The model may actually be unbounded: Gurobi returned "
"GRB_INF_OR_UNBD");
ABSL_FALLTHROUGH_INTENDED;
case GRB_INFEASIBLE:
response.set_status(MPSOLVER_INFEASIBLE);
break;
case GRB_UNBOUNDED:
response.set_status(MPSOLVER_UNBOUNDED);
break;
default: {
if (solution_count > 0) {
response.set_status(MPSOLVER_FEASIBLE);
} else {
response.set_status(MPSOLVER_NOT_SOLVED);
response.set_status_str(
absl::StrFormat("Gurobi status code %d", optimization_status));
}
break;
}
}
if (solution_count > 0 && (response.status() == MPSOLVER_FEASIBLE ||
response.status() == MPSOLVER_OPTIMAL)) {
double objective_value = 0;
RETURN_IF_GUROBI_ERROR(
GRBgetdblattr(gurobi_model, GRB_DBL_ATTR_OBJVAL, &objective_value));
response.set_objective_value(objective_value);
double best_objective_bound = 0;
const int error = GRBgetdblattr(gurobi_model, GRB_DBL_ATTR_OBJBOUND,
&best_objective_bound);
if (response.status() == MPSOLVER_OPTIMAL &&
error == GRB_ERROR_DATA_NOT_AVAILABLE) {
// If the presolve deletes all variables, there's no best bound.
response.set_best_objective_bound(objective_value);
} else {
RETURN_IF_GUROBI_ERROR(error);
response.set_best_objective_bound(best_objective_bound);
}
response.mutable_variable_value()->Resize(variable_size, 0);
RETURN_IF_GUROBI_ERROR(
GRBgetdblattrarray(gurobi_model, GRB_DBL_ATTR_X, 0, variable_size,
response.mutable_variable_value()->mutable_data()));
// NOTE, GurobiSolveProto() is exposed to external clients via MPSolver API,
// which assumes the solution values of integer variables are rounded to
// integer values.
auto round_values_of_integer_variables_fn =
[&](google::protobuf::RepeatedField<double>* values) {
for (int v = 0; v < variable_size; ++v) {
if (model.variable(v).is_integer()) {
(*values)[v] = std::round((*values)[v]);
}
}
};
round_values_of_integer_variables_fn(response.mutable_variable_value());
if (!has_integer_variables && model.general_constraint_size() == 0) {
response.mutable_dual_value()->Resize(model.constraint_size(), 0);
RETURN_IF_GUROBI_ERROR(GRBgetdblattrarray(
gurobi_model, GRB_DBL_ATTR_PI, 0, model.constraint_size(),
response.mutable_dual_value()->mutable_data()));
}
const int additional_solutions = std::min(
solution_count, std::min(request.populate_additional_solutions_up_to(),
std::numeric_limits<int32_t>::max() - 1) +
1);
for (int i = 1; i < additional_solutions; ++i) {
RETURN_IF_GUROBI_ERROR(
GRBsetintparam(model_env, GRB_INT_PAR_SOLUTIONNUMBER, i));
MPSolution* solution = response.add_additional_solutions();
solution->mutable_variable_value()->Resize(variable_size, 0);
double objective_value = 0;
RETURN_IF_GUROBI_ERROR(GRBgetdblattr(
gurobi_model, GRB_DBL_ATTR_POOLOBJVAL, &objective_value));
solution->set_objective_value(objective_value);
RETURN_IF_GUROBI_ERROR(GRBgetdblattrarray(
gurobi_model, GRB_DBL_ATTR_XN, 0, variable_size,
solution->mutable_variable_value()->mutable_data()));
round_values_of_integer_variables_fn(solution->mutable_variable_value());
}
}
#undef RETURN_IF_GUROBI_ERROR
return response;
}
} // namespace operations_research