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ortools-clone/ortools/constraint_solver/default_search.cc
Corentin Le Molgat a66a6daac7 Bump Copyright to 2025
2025-01-10 11:35:44 +01:00

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// Copyright 2010-2025 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 <cstddef>
#include <cstdint>
#include <functional>
#include <limits>
#include <memory>
#include <random>
#include <string>
#include <utility>
#include <vector>
#include "absl/container/flat_hash_set.h"
#include "absl/strings/str_format.h"
#include "ortools/base/commandlineflags.h"
#include "ortools/base/logging.h"
#include "ortools/base/stl_util.h"
#include "ortools/base/types.h"
#include "ortools/constraint_solver/constraint_solver.h"
#include "ortools/constraint_solver/constraint_solveri.h"
#include "ortools/util/cached_log.h"
#include "ortools/util/string_array.h"
ABSL_FLAG(int, cp_impact_divider, 10, "Divider for continuous update.");
namespace operations_research {
namespace {
// Default constants for search phase parameters.
const int kDefaultNumberOfSplits = 100;
const int kDefaultHeuristicPeriod = 100;
const int kDefaultHeuristicNumFailuresLimit = 30;
const bool kDefaultUseLastConflict = true;
} // namespace
DefaultPhaseParameters::DefaultPhaseParameters()
: var_selection_schema(DefaultPhaseParameters::CHOOSE_MAX_SUM_IMPACT),
value_selection_schema(DefaultPhaseParameters::SELECT_MIN_IMPACT),
initialization_splits(kDefaultNumberOfSplits),
run_all_heuristics(true),
heuristic_period(kDefaultHeuristicPeriod),
heuristic_num_failures_limit(kDefaultHeuristicNumFailuresLimit),
persistent_impact(true),
random_seed(CpRandomSeed()),
display_level(DefaultPhaseParameters::NORMAL),
use_last_conflict(kDefaultUseLastConflict),
decision_builder(nullptr) {}
namespace {
// ----- DomainWatcher -----
// This class follows the domains of variables and will report the log of the
// search space of all integer variables.
class DomainWatcher {
public:
DomainWatcher(const std::vector<IntVar*>& vars, int cache_size)
: vars_(vars) {
cached_log_.Init(cache_size);
}
// This type is neither copyable nor movable.
DomainWatcher(const DomainWatcher&) = delete;
DomainWatcher& operator=(const DomainWatcher&) = delete;
double LogSearchSpaceSize() {
double result = 0.0;
for (int index = 0; index < vars_.size(); ++index) {
result += cached_log_.Log2(vars_[index]->Size());
}
return result;
}
double Log2(int64_t size) const { return cached_log_.Log2(size); }
private:
std::vector<IntVar*> vars_;
CachedLog cached_log_;
};
// ---------- FindVar decision visitor ---------
class FindVar : public DecisionVisitor {
public:
enum Operation { NONE, ASSIGN, SPLIT_LOW, SPLIT_HIGH };
FindVar() : var_(nullptr), value_(0), operation_(NONE) {}
~FindVar() override {}
void VisitSetVariableValue(IntVar* var, int64_t value) override {
var_ = var;
value_ = value;
operation_ = ASSIGN;
}
void VisitSplitVariableDomain(IntVar* var, int64_t value,
bool start_with_lower_half) override {
var_ = var;
value_ = value;
operation_ = start_with_lower_half ? SPLIT_LOW : SPLIT_HIGH;
}
void VisitScheduleOrPostpone(IntervalVar* const var, int64_t est) override {
operation_ = NONE;
}
virtual void VisitTryRankFirst(SequenceVar* const sequence, int index) {
operation_ = NONE;
}
virtual void VisitTryRankLast(SequenceVar* const sequence, int index) {
operation_ = NONE;
}
void VisitUnknownDecision() override { operation_ = NONE; }
// Returns the current variable.
IntVar* var() const {
CHECK_NE(operation_, NONE);
return var_;
}
// Returns the value of the current variable.
int64_t value() const {
CHECK_NE(operation_, NONE);
return value_;
}
Operation operation() const { return operation_; }
std::string DebugString() const override {
return "FindVar decision visitor";
}
private:
IntVar* var_;
int64_t value_;
Operation operation_;
};
// ----- Auxiliary decision builders to init impacts -----
// This class initialize impacts by scanning each value of the domain
// of the variable.
class InitVarImpacts : public DecisionBuilder {
public:
// ----- main -----
InitVarImpacts()
: var_(nullptr),
update_impact_callback_(nullptr),
new_start_(false),
var_index_(0),
value_index_(-1),
update_impact_closure_([this]() { UpdateImpacts(); }),
updater_(update_impact_closure_) {
CHECK(update_impact_closure_ != nullptr);
}
~InitVarImpacts() override {}
void UpdateImpacts() {
// the Min is always the value we just set.
update_impact_callback_(var_index_, var_->Min());
}
void Init(IntVar* const var, IntVarIterator* const iterator, int var_index) {
var_ = var;
iterator_ = iterator;
var_index_ = var_index;
new_start_ = true;
value_index_ = 0;
}
Decision* Next(Solver* const solver) override {
CHECK(var_ != nullptr);
CHECK(iterator_ != nullptr);
if (new_start_) {
active_values_.clear();
for (const int64_t value : InitAndGetValues(iterator_)) {
active_values_.push_back(value);
}
new_start_ = false;
}
if (value_index_ == active_values_.size()) {
return nullptr;
}
updater_.var_ = var_;
updater_.value_ = active_values_[value_index_];
value_index_++;
return &updater_;
}
void set_update_impact_callback(std::function<void(int, int64_t)> callback) {
update_impact_callback_ = std::move(callback);
}
private:
// ----- helper decision -----
class AssignCallFail : public Decision {
public:
explicit AssignCallFail(const std::function<void()>& update_impact_closure)
: var_(nullptr),
value_(0),
update_impact_closure_(update_impact_closure) {
CHECK(update_impact_closure_ != nullptr);
}
// This type is neither copyable nor movable.
AssignCallFail(const AssignCallFail&) = delete;
AssignCallFail& operator=(const AssignCallFail&) = delete;
~AssignCallFail() override {}
void Apply(Solver* const solver) override {
CHECK(var_ != nullptr);
var_->SetValue(value_);
// We call the closure on the part that cannot fail.
update_impact_closure_();
solver->Fail();
}
void Refute(Solver* const solver) override {}
// Public data for easy access.
IntVar* var_;
int64_t value_;
private:
const std::function<void()>& update_impact_closure_;
};
IntVar* var_;
std::function<void(int, int64_t)> update_impact_callback_;
bool new_start_;
IntVarIterator* iterator_;
int var_index_;
std::vector<int64_t> active_values_;
int value_index_;
std::function<void()> update_impact_closure_;
AssignCallFail updater_;
};
// This class initialize impacts by scanning at most 'split_size'
// intervals on the domain of the variable.
class InitVarImpactsWithSplits : public DecisionBuilder {
public:
// ----- helper decision -----
class AssignIntervalCallFail : public Decision {
public:
explicit AssignIntervalCallFail(
const std::function<void()>& update_impact_closure)
: var_(nullptr),
value_min_(0),
value_max_(0),
update_impact_closure_(update_impact_closure) {
CHECK(update_impact_closure_ != nullptr);
}
// This type is neither copyable nor movable.
AssignIntervalCallFail(const AssignIntervalCallFail&) = delete;
AssignIntervalCallFail& operator=(const AssignIntervalCallFail&) = delete;
~AssignIntervalCallFail() override {}
void Apply(Solver* const solver) override {
CHECK(var_ != nullptr);
var_->SetRange(value_min_, value_max_);
// We call the closure on the part that cannot fail.
update_impact_closure_();
solver->Fail();
}
void Refute(Solver* const solver) override {}
// Public for easy access.
IntVar* var_;
int64_t value_min_;
int64_t value_max_;
private:
const std::function<void()>& update_impact_closure_;
};
// ----- main -----
explicit InitVarImpactsWithSplits(int split_size)
: var_(nullptr),
update_impact_callback_(nullptr),
new_start_(false),
var_index_(0),
min_value_(0),
max_value_(0),
split_size_(split_size),
split_index_(-1),
update_impact_closure_([this]() { UpdateImpacts(); }),
updater_(update_impact_closure_) {
CHECK(update_impact_closure_ != nullptr);
}
~InitVarImpactsWithSplits() override {}
void UpdateImpacts() {
for (const int64_t value : InitAndGetValues(iterator_)) {
update_impact_callback_(var_index_, value);
}
}
void Init(IntVar* const var, IntVarIterator* const iterator, int var_index) {
var_ = var;
iterator_ = iterator;
var_index_ = var_index;
new_start_ = true;
split_index_ = 0;
}
int64_t IntervalStart(int index) const {
const int64_t length = max_value_ - min_value_ + 1;
return (min_value_ + length * index / split_size_);
}
Decision* Next(Solver* const solver) override {
if (new_start_) {
min_value_ = var_->Min();
max_value_ = var_->Max();
new_start_ = false;
}
if (split_index_ == split_size_) {
return nullptr;
}
updater_.var_ = var_;
updater_.value_min_ = IntervalStart(split_index_);
split_index_++;
if (split_index_ == split_size_) {
updater_.value_max_ = max_value_;
} else {
updater_.value_max_ = IntervalStart(split_index_) - 1;
}
return &updater_;
}
void set_update_impact_callback(std::function<void(int, int64_t)> callback) {
update_impact_callback_ = std::move(callback);
}
private:
IntVar* var_;
std::function<void(int, int64_t)> update_impact_callback_;
bool new_start_;
IntVarIterator* iterator_;
int var_index_;
int64_t min_value_;
int64_t max_value_;
const int split_size_;
int split_index_;
std::function<void()> update_impact_closure_;
AssignIntervalCallFail updater_;
};
// ----- ImpactRecorder
// This class will record the impacts of all assignment of values to
// variables. Its main output is to find the optimal pair (variable/value)
// based on default phase parameters.
class ImpactRecorder : public SearchMonitor {
public:
static const int kLogCacheSize;
static const double kPerfectImpact;
static const double kFailureImpact;
static const double kInitFailureImpact;
static const int kUninitializedVarIndex;
ImpactRecorder(Solver* const solver, DomainWatcher* const domain_watcher,
const std::vector<IntVar*>& vars,
DefaultPhaseParameters::DisplayLevel display_level)
: SearchMonitor(solver),
domain_watcher_(domain_watcher),
vars_(vars),
size_(vars.size()),
current_log_space_(0.0),
impacts_(size_),
original_min_(size_, 0LL),
domain_iterators_(new IntVarIterator*[size_]),
display_level_(display_level),
current_var_(kUninitializedVarIndex),
current_value_(0),
init_done_(false) {
for (int i = 0; i < size_; ++i) {
domain_iterators_[i] = vars_[i]->MakeDomainIterator(true);
var_map_[vars_[i]] = i;
}
}
// This type is neither copyable nor movable.
ImpactRecorder(const ImpactRecorder&) = delete;
ImpactRecorder& operator=(const ImpactRecorder&) = delete;
void ApplyDecision(Decision* const d) override {
if (!init_done_) {
return;
}
d->Accept(&find_var_);
if (find_var_.operation() == FindVar::ASSIGN &&
var_map_.contains(find_var_.var())) {
current_var_ = var_map_[find_var_.var()];
current_value_ = find_var_.value();
current_log_space_ = domain_watcher_->LogSearchSpaceSize();
} else {
current_var_ = kUninitializedVarIndex;
current_value_ = 0;
}
}
void AfterDecision(Decision* const d, bool apply) override {
if (init_done_ && current_var_ != kUninitializedVarIndex) {
if (current_log_space_ > 0.0) {
const double log_space = domain_watcher_->LogSearchSpaceSize();
if (apply) {
const double impact = kPerfectImpact - log_space / current_log_space_;
UpdateImpact(current_var_, current_value_, impact);
current_var_ = kUninitializedVarIndex;
current_value_ = 0;
}
current_log_space_ = log_space;
}
}
}
void BeginFail() override {
if (init_done_ && current_var_ != kUninitializedVarIndex) {
UpdateImpact(current_var_, current_value_, kFailureImpact);
current_var_ = kUninitializedVarIndex;
current_value_ = 0;
}
}
void ResetAllImpacts() {
for (int i = 0; i < size_; ++i) {
original_min_[i] = vars_[i]->Min();
// By default, we init impacts to 2.0 -> equivalent to failure.
// This will be overwritten to real impact values on valid domain
// values during the FirstRun() method.
impacts_[i].resize(vars_[i]->Max() - vars_[i]->Min() + 1,
kInitFailureImpact);
}
for (int i = 0; i < size_; ++i) {
for (int j = 0; j < impacts_[i].size(); ++j) {
impacts_[i][j] = kInitFailureImpact;
}
}
}
void UpdateImpact(int var_index, int64_t value, double impact) {
const int64_t value_index = value - original_min_[var_index];
const double current_impact = impacts_[var_index][value_index];
const double new_impact =
(current_impact * (absl::GetFlag(FLAGS_cp_impact_divider) - 1) +
impact) /
absl::GetFlag(FLAGS_cp_impact_divider);
impacts_[var_index][value_index] = new_impact;
}
void InitImpact(int var_index, int64_t value) {
const double log_space = domain_watcher_->LogSearchSpaceSize();
const double impact = kPerfectImpact - log_space / current_log_space_;
const int64_t value_index = value - original_min_[var_index];
DCHECK_LT(var_index, size_);
DCHECK_LT(value_index, impacts_[var_index].size());
impacts_[var_index][value_index] = impact;
init_count_++;
}
void FirstRun(int64_t splits) {
Solver* const s = solver();
current_log_space_ = domain_watcher_->LogSearchSpaceSize();
if (display_level_ != DefaultPhaseParameters::NONE) {
LOG(INFO) << " - initial log2(SearchSpace) = " << current_log_space_;
}
const int64_t init_time = s->wall_time();
ResetAllImpacts();
int64_t removed_counter = 0;
FirstRunVariableContainers* container =
s->RevAlloc(new FirstRunVariableContainers(this, splits));
// Loop on the variables, scan domains and initialize impacts.
for (int var_index = 0; var_index < size_; ++var_index) {
IntVar* const var = vars_[var_index];
if (var->Bound()) {
continue;
}
IntVarIterator* const iterator = domain_iterators_[var_index];
DecisionBuilder* init_decision_builder = nullptr;
const bool no_split = var->Size() < splits;
if (no_split) {
// The domain is small enough, we scan it completely.
container->without_split()->set_update_impact_callback(
container->update_impact_callback());
container->without_split()->Init(var, iterator, var_index);
init_decision_builder = container->without_split();
} else {
// The domain is too big, we scan it in initialization_splits
// intervals.
container->with_splits()->set_update_impact_callback(
container->update_impact_callback());
container->with_splits()->Init(var, iterator, var_index);
init_decision_builder = container->with_splits();
}
// Reset the number of impacts initialized.
init_count_ = 0;
// Use Solve() to scan all values of one variable.
s->Solve(init_decision_builder);
// If we have not initialized all values, then they can be removed.
// As the iterator is not stable w.r.t. deletion, we need to store
// removed values in an intermediate vector.
if (init_count_ != var->Size() && no_split) {
container->ClearRemovedValues();
for (const int64_t value : InitAndGetValues(iterator)) {
const int64_t value_index = value - original_min_[var_index];
if (impacts_[var_index][value_index] == kInitFailureImpact) {
container->PushBackRemovedValue(value);
}
}
CHECK(container->HasRemovedValues()) << var->DebugString();
removed_counter += container->NumRemovedValues();
const double old_log = domain_watcher_->Log2(var->Size());
var->RemoveValues(container->removed_values());
current_log_space_ += domain_watcher_->Log2(var->Size()) - old_log;
}
}
if (display_level_ != DefaultPhaseParameters::NONE) {
if (removed_counter) {
LOG(INFO) << " - init done, time = " << s->wall_time() - init_time
<< " ms, " << removed_counter
<< " values removed, log2(SearchSpace) = "
<< current_log_space_;
} else {
LOG(INFO) << " - init done, time = " << s->wall_time() - init_time
<< " ms";
}
}
s->SaveAndSetValue(&init_done_, true);
}
// This method scans the domain of one variable and returns the sum
// of the impacts of all values in its domain, along with the value
// with minimal impact.
void ScanVarImpacts(int var_index, int64_t* const best_impact_value,
double* const var_impacts,
DefaultPhaseParameters::VariableSelection var_select,
DefaultPhaseParameters::ValueSelection value_select) {
CHECK(best_impact_value != nullptr);
CHECK(var_impacts != nullptr);
double max_impact = -std::numeric_limits<double>::max();
double min_impact = std::numeric_limits<double>::max();
double sum_var_impact = 0.0;
int64_t min_impact_value = -1;
int64_t max_impact_value = -1;
for (const int64_t value : InitAndGetValues(domain_iterators_[var_index])) {
const int64_t value_index = value - original_min_[var_index];
DCHECK_LT(var_index, size_);
DCHECK_LT(value_index, impacts_[var_index].size());
const double current_impact = impacts_[var_index][value_index];
sum_var_impact += current_impact;
if (current_impact > max_impact) {
max_impact = current_impact;
max_impact_value = value;
}
if (current_impact < min_impact) {
min_impact = current_impact;
min_impact_value = value;
}
}
switch (var_select) {
case DefaultPhaseParameters::CHOOSE_MAX_AVERAGE_IMPACT: {
*var_impacts = sum_var_impact / vars_[var_index]->Size();
break;
}
case DefaultPhaseParameters::CHOOSE_MAX_VALUE_IMPACT: {
*var_impacts = max_impact;
break;
}
default: {
*var_impacts = sum_var_impact;
break;
}
}
switch (value_select) {
case DefaultPhaseParameters::SELECT_MIN_IMPACT: {
*best_impact_value = min_impact_value;
break;
}
case DefaultPhaseParameters::SELECT_MAX_IMPACT: {
*best_impact_value = max_impact_value;
break;
}
}
}
std::string DebugString() const override { return "ImpactRecorder"; }
private:
// A container for the variables needed in FirstRun that is reversibly
// allocable.
class FirstRunVariableContainers : public BaseObject {
public:
FirstRunVariableContainers(ImpactRecorder* impact_recorder, int64_t splits)
: update_impact_callback_(
[impact_recorder](int var_index, int64_t value) {
impact_recorder->InitImpact(var_index, value);
}),
removed_values_(),
without_splits_(),
with_splits_(splits) {}
std::function<void(int, int64_t)> update_impact_callback() const {
return update_impact_callback_;
}
void PushBackRemovedValue(int64_t value) {
removed_values_.push_back(value);
}
bool HasRemovedValues() const { return !removed_values_.empty(); }
void ClearRemovedValues() { removed_values_.clear(); }
size_t NumRemovedValues() const { return removed_values_.size(); }
const std::vector<int64_t>& removed_values() const {
return removed_values_;
}
InitVarImpacts* without_split() { return &without_splits_; }
InitVarImpactsWithSplits* with_splits() { return &with_splits_; }
std::string DebugString() const override {
return "FirstRunVariableContainers";
}
private:
const std::function<void(int, int64_t)> update_impact_callback_;
std::vector<int64_t> removed_values_;
InitVarImpacts without_splits_;
InitVarImpactsWithSplits with_splits_;
};
DomainWatcher* const domain_watcher_;
std::vector<IntVar*> vars_;
const int size_;
double current_log_space_;
// impacts_[i][j] stores the average search space reduction when assigning
// original_min_[i] + j to variable i.
std::vector<std::vector<double> > impacts_;
std::vector<int64_t> original_min_;
std::unique_ptr<IntVarIterator*[]> domain_iterators_;
int64_t init_count_;
const DefaultPhaseParameters::DisplayLevel display_level_;
int current_var_;
int64_t current_value_;
FindVar find_var_;
absl::flat_hash_map<const IntVar*, int> var_map_;
bool init_done_;
};
const int ImpactRecorder::kLogCacheSize = 1000;
const double ImpactRecorder::kPerfectImpact = 1.0;
const double ImpactRecorder::kFailureImpact = 1.0;
const double ImpactRecorder::kInitFailureImpact = 2.0;
const int ImpactRecorder::kUninitializedVarIndex = -1;
// This structure stores 'var[index] (left?==:!=) value'.
class ChoiceInfo {
public:
ChoiceInfo() : value_(0), var_(nullptr), left_(false) {}
ChoiceInfo(IntVar* const var, int64_t value, bool left)
: value_(value), var_(var), left_(left) {}
std::string DebugString() const {
return absl::StrFormat("%s %s %d", var_->name(), (left_ ? "==" : "!="),
value_);
}
IntVar* var() const { return var_; }
bool left() const { return left_; }
int64_t value() const { return value_; }
void set_left(bool left) { left_ = left; }
private:
int64_t value_;
IntVar* var_;
bool left_;
};
// ---------- Heuristics ----------
class RunHeuristicsAsDives : public Decision {
public:
RunHeuristicsAsDives(Solver* const solver, const std::vector<IntVar*>& vars,
DefaultPhaseParameters::DisplayLevel level,
bool run_all_heuristics, int random_seed,
int heuristic_period, int heuristic_num_failures_limit)
: heuristic_limit_(nullptr),
display_level_(level),
run_all_heuristics_(run_all_heuristics),
random_(random_seed),
heuristic_period_(heuristic_period),
heuristic_branch_count_(0),
heuristic_runs_(0) {
Init(solver, vars, heuristic_num_failures_limit);
}
~RunHeuristicsAsDives() override { gtl::STLDeleteElements(&heuristics_); }
void Apply(Solver* const solver) override {
if (!RunAllHeuristics(solver)) {
solver->Fail();
}
}
void Refute(Solver* const solver) override {}
bool ShouldRun() {
if (heuristic_period_ <= 0) {
return false;
}
++heuristic_branch_count_;
return heuristic_branch_count_ % heuristic_period_ == 0;
}
bool RunOneHeuristic(Solver* const solver, int index) {
HeuristicWrapper* const wrapper = heuristics_[index];
heuristic_runs_++;
const bool result =
solver->SolveAndCommit(wrapper->phase, heuristic_limit_);
if (result && display_level_ != DefaultPhaseParameters::NONE) {
LOG(INFO) << " --- solution found by heuristic " << wrapper->name
<< " --- ";
}
return result;
}
bool RunAllHeuristics(Solver* const solver) {
if (run_all_heuristics_) {
for (int index = 0; index < heuristics_.size(); ++index) {
for (int run = 0; run < heuristics_[index]->runs; ++run) {
if (RunOneHeuristic(solver, index)) {
return true;
}
}
}
return false;
} else {
DCHECK_GT(heuristics_.size(), 0);
const int index = absl::Uniform<int>(random_, 0, heuristics_.size());
return RunOneHeuristic(solver, index);
}
}
int Rand32(int size) {
DCHECK_GT(size, 0);
return absl::Uniform<int>(random_, 0, size);
}
void Init(Solver* const solver, const std::vector<IntVar*>& vars,
int heuristic_num_failures_limit) {
const int kRunOnce = 1;
const int kRunMore = 2;
const int kRunALot = 3;
heuristics_.push_back(new HeuristicWrapper(
solver, vars, Solver::CHOOSE_MIN_SIZE_LOWEST_MIN,
Solver::ASSIGN_MIN_VALUE, "AssignMinValueToMinDomainSize", kRunOnce));
heuristics_.push_back(new HeuristicWrapper(
solver, vars, Solver::CHOOSE_MIN_SIZE_HIGHEST_MAX,
Solver::ASSIGN_MAX_VALUE, "AssignMaxValueToMinDomainSize", kRunOnce));
heuristics_.push_back(
new HeuristicWrapper(solver, vars, Solver::CHOOSE_MIN_SIZE_LOWEST_MIN,
Solver::ASSIGN_CENTER_VALUE,
"AssignCenterValueToMinDomainSize", kRunOnce));
heuristics_.push_back(new HeuristicWrapper(
solver, vars, Solver::CHOOSE_FIRST_UNBOUND, Solver::ASSIGN_RANDOM_VALUE,
"AssignRandomValueToFirstUnbound", kRunALot));
heuristics_.push_back(new HeuristicWrapper(
solver, vars, Solver::CHOOSE_RANDOM, Solver::ASSIGN_MIN_VALUE,
"AssignMinValueToRandomVariable", kRunMore));
heuristics_.push_back(new HeuristicWrapper(
solver, vars, Solver::CHOOSE_RANDOM, Solver::ASSIGN_MAX_VALUE,
"AssignMaxValueToRandomVariable", kRunMore));
heuristics_.push_back(new HeuristicWrapper(
solver, vars, Solver::CHOOSE_RANDOM, Solver::ASSIGN_RANDOM_VALUE,
"AssignRandomValueToRandomVariable", kRunMore));
heuristic_limit_ = solver->MakeFailuresLimit(heuristic_num_failures_limit);
}
int heuristic_runs() const { return heuristic_runs_; }
private:
// This class wraps one heuristic with extra information: name and
// number of runs.
struct HeuristicWrapper {
HeuristicWrapper(Solver* const solver, const std::vector<IntVar*>& vars,
Solver::IntVarStrategy var_strategy,
Solver::IntValueStrategy value_strategy,
const std::string& heuristic_name, int heuristic_runs)
: phase(solver->MakePhase(vars, var_strategy, value_strategy)),
name(heuristic_name),
runs(heuristic_runs) {}
// The decision builder we are going to use in this dive.
DecisionBuilder* const phase;
// A name for logging purposes.
const std::string name;
// How many times we will run this particular heuristic in case the
// parameter run_all_heuristics is true. This is useful for random
// heuristics where it makes sense to run them more than once.
const int runs;
};
std::vector<HeuristicWrapper*> heuristics_;
SearchMonitor* heuristic_limit_;
DefaultPhaseParameters::DisplayLevel display_level_;
bool run_all_heuristics_;
std::mt19937 random_;
const int heuristic_period_;
int heuristic_branch_count_;
int heuristic_runs_;
};
// ---------- DefaultIntegerSearch ----------
// Default phase decision builder.
class DefaultIntegerSearch : public DecisionBuilder {
public:
static const double kSmallSearchSpaceLimit;
DefaultIntegerSearch(Solver* const solver, const std::vector<IntVar*>& vars,
const DefaultPhaseParameters& parameters)
: vars_(vars),
parameters_(parameters),
domain_watcher_(vars, ImpactRecorder::kLogCacheSize),
impact_recorder_(solver, &domain_watcher_, vars,
parameters.display_level),
heuristics_(solver, vars_, parameters_.display_level,
parameters_.run_all_heuristics, parameters_.random_seed,
parameters_.heuristic_period,
parameters_.heuristic_num_failures_limit),
find_var_(),
last_int_var_(nullptr),
last_int_value_(0),
last_operation_(FindVar::NONE),
last_conflict_count_(0),
init_done_(false) {}
~DefaultIntegerSearch() override {}
Decision* Next(Solver* const solver) override {
CheckInit(solver);
if (heuristics_.ShouldRun()) {
return &heuristics_;
}
Decision* const decision = parameters_.decision_builder != nullptr
? parameters_.decision_builder->Next(solver)
: ImpactNext(solver);
// Returns early if the search tree is finished anyway.
if (decision == nullptr) {
ClearLastDecision();
return nullptr;
}
// The main goal of last conflict is to branch on a decision
// variable different from the one being evaluated. We need to
// retrieve first the variable in the current decision.
decision->Accept(&find_var_);
IntVar* const decision_var =
find_var_.operation() != FindVar::NONE ? find_var_.var() : nullptr;
// We will hijack the search heuristics if
// - we use last conflict
// - we have stored the last decision from the search heuristics
// - the variable stored is different from the variable of the current
// decision
// - this variable is not bound already
// Furthermore, each case will also verify that the stored decision is
// compatible with the current domain variable.
if (parameters_.use_last_conflict && last_int_var_ != nullptr &&
!last_int_var_->Bound() &&
(decision_var == nullptr || decision_var != last_int_var_)) {
switch (last_operation_) {
case FindVar::ASSIGN: {
if (last_int_var_->Contains(last_int_value_)) {
Decision* const assign =
solver->MakeAssignVariableValue(last_int_var_, last_int_value_);
ClearLastDecision();
last_conflict_count_++;
return assign;
}
break;
}
case FindVar::SPLIT_LOW: {
if (last_int_var_->Max() > last_int_value_ &&
last_int_var_->Min() <= last_int_value_) {
Decision* const split = solver->MakeVariableLessOrEqualValue(
last_int_var_, last_int_value_);
ClearLastDecision();
last_conflict_count_++;
return split;
}
break;
}
case FindVar::SPLIT_HIGH: {
if (last_int_var_->Min() < last_int_value_ &&
last_int_var_->Max() >= last_int_value_) {
Decision* const split = solver->MakeVariableGreaterOrEqualValue(
last_int_var_, last_int_value_);
ClearLastDecision();
last_conflict_count_++;
return split;
}
break;
}
default: {
break;
}
}
}
if (parameters_.use_last_conflict) {
// Store the last decision to replay it upon failure.
decision->Accept(&find_var_);
if (find_var_.operation() != FindVar::NONE) {
last_int_var_ = find_var_.var();
last_int_value_ = find_var_.value();
last_operation_ = find_var_.operation();
}
}
return decision;
}
void ClearLastDecision() {
last_int_var_ = nullptr;
last_int_value_ = 0;
last_operation_ = FindVar::NONE;
}
void AppendMonitors(Solver* const solver,
std::vector<SearchMonitor*>* const extras) override {
CHECK(solver != nullptr);
CHECK(extras != nullptr);
if (parameters_.decision_builder == nullptr) {
extras->push_back(&impact_recorder_);
}
}
void Accept(ModelVisitor* const visitor) const override {
visitor->BeginVisitExtension(ModelVisitor::kVariableGroupExtension);
visitor->VisitIntegerVariableArrayArgument(ModelVisitor::kVarsArgument,
vars_);
visitor->EndVisitExtension(ModelVisitor::kVariableGroupExtension);
}
std::string DebugString() const override {
std::string out = "DefaultIntegerSearch(";
if (parameters_.decision_builder == nullptr) {
out.append("Impact Based Search, ");
} else {
out.append(parameters_.decision_builder->DebugString());
out.append(", ");
}
out.append(JoinDebugStringPtr(vars_, ", "));
out.append(")");
return out;
}
std::string StatString() const {
const int runs = heuristics_.heuristic_runs();
std::string result;
if (runs > 0) {
if (!result.empty()) {
result.append(", ");
}
if (runs == 1) {
result.append("1 heuristic run");
} else {
absl::StrAppendFormat(&result, "%d heuristic runs", runs);
}
}
if (last_conflict_count_ > 0) {
if (!result.empty()) {
result.append(", ");
}
if (last_conflict_count_ == 1) {
result.append("1 last conflict hint");
} else {
absl::StrAppendFormat(&result, "%d last conflict hints",
last_conflict_count_);
}
}
return result;
}
private:
void CheckInit(Solver* const solver) {
if (init_done_) {
return;
}
if (parameters_.decision_builder == nullptr) {
// Decide if we are doing impacts, no if one variable is too big.
for (int i = 0; i < vars_.size(); ++i) {
if (vars_[i]->Max() - vars_[i]->Min() > 0xFFFFFF) {
if (parameters_.display_level == DefaultPhaseParameters::VERBOSE) {
LOG(INFO) << "Domains are too large, switching to simple "
<< "heuristics";
}
solver->SaveValue(
reinterpret_cast<void**>(&parameters_.decision_builder));
parameters_.decision_builder =
solver->MakePhase(vars_, Solver::CHOOSE_MIN_SIZE_LOWEST_MIN,
Solver::ASSIGN_MIN_VALUE);
solver->SaveAndSetValue(&init_done_, true);
return;
}
}
// No if the search space is too small.
if (domain_watcher_.LogSearchSpaceSize() < kSmallSearchSpaceLimit) {
if (parameters_.display_level == DefaultPhaseParameters::VERBOSE) {
LOG(INFO) << "Search space is too small, switching to simple "
<< "heuristics";
}
solver->SaveValue(
reinterpret_cast<void**>(&parameters_.decision_builder));
parameters_.decision_builder = solver->MakePhase(
vars_, Solver::CHOOSE_FIRST_UNBOUND, Solver::ASSIGN_MIN_VALUE);
solver->SaveAndSetValue(&init_done_, true);
return;
}
if (parameters_.display_level != DefaultPhaseParameters::NONE) {
LOG(INFO) << "Init impact based search phase on " << vars_.size()
<< " variables, initialization splits = "
<< parameters_.initialization_splits
<< ", heuristic_period = " << parameters_.heuristic_period
<< ", run_all_heuristics = "
<< parameters_.run_all_heuristics;
}
// Init the impacts.
impact_recorder_.FirstRun(parameters_.initialization_splits);
}
if (parameters_.persistent_impact) {
init_done_ = true;
} else {
solver->SaveAndSetValue(&init_done_, true);
}
}
// This method will do an exhaustive scan of all domains of all
// variables to select the variable with the maximal sum of impacts
// per value in its domain, and then select the value with the
// minimal impact.
Decision* ImpactNext(Solver* const solver) {
IntVar* var = nullptr;
int64_t value = 0;
double best_var_impact = -std::numeric_limits<double>::max();
for (int i = 0; i < vars_.size(); ++i) {
if (!vars_[i]->Bound()) {
int64_t current_value = 0;
double current_var_impact = 0.0;
impact_recorder_.ScanVarImpacts(i, &current_value, &current_var_impact,
parameters_.var_selection_schema,
parameters_.value_selection_schema);
if (current_var_impact > best_var_impact) {
var = vars_[i];
value = current_value;
best_var_impact = current_var_impact;
}
}
}
if (var == nullptr) {
return nullptr;
} else {
return solver->MakeAssignVariableValue(var, value);
}
}
// ----- data members -----
std::vector<IntVar*> vars_;
DefaultPhaseParameters parameters_;
DomainWatcher domain_watcher_;
ImpactRecorder impact_recorder_;
RunHeuristicsAsDives heuristics_;
FindVar find_var_;
IntVar* last_int_var_;
int64_t last_int_value_;
FindVar::Operation last_operation_;
int last_conflict_count_;
bool init_done_;
};
const double DefaultIntegerSearch::kSmallSearchSpaceLimit = 10.0;
} // namespace
// ---------- API ----------
std::string DefaultPhaseStatString(DecisionBuilder* db) {
DefaultIntegerSearch* const dis = dynamic_cast<DefaultIntegerSearch*>(db);
return dis != nullptr ? dis->StatString() : "";
}
DecisionBuilder* Solver::MakeDefaultPhase(const std::vector<IntVar*>& vars) {
DefaultPhaseParameters parameters;
return MakeDefaultPhase(vars, parameters);
}
DecisionBuilder* Solver::MakeDefaultPhase(
const std::vector<IntVar*>& vars,
const DefaultPhaseParameters& parameters) {
return RevAlloc(new DefaultIntegerSearch(this, vars, parameters));
}
} // namespace operations_research
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