always-cautious/ortools-clone
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity
Files
0fe7cb5dbd486c15f26fb19b331a0e541eadb259
ortools-clone/ortools/sat/disjunctive.cc
Corentin Le Molgat 1b4d75ceb3 sat: backport from main
2025-11-05 13:55:12 +01:00

1953 lines
75 KiB
C++
Raw Blame History

// 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 "ortools/sat/disjunctive.h"
#include <algorithm>
#include <cstdint>
#include <utility>
#include <vector>
#include "absl/algorithm/container.h"
#include "absl/base/log_severity.h"
#include "absl/cleanup/cleanup.h"
#include "absl/log/check.h"
#include "absl/log/log.h"
#include "absl/types/span.h"
#include "ortools/sat/all_different.h"
#include "ortools/sat/integer.h"
#include "ortools/sat/integer_base.h"
#include "ortools/sat/intervals.h"
#include "ortools/sat/linear_propagation.h"
#include "ortools/sat/model.h"
#include "ortools/sat/precedences.h"
#include "ortools/sat/sat_base.h"
#include "ortools/sat/sat_parameters.pb.h"
#include "ortools/sat/scheduling_helpers.h"
#include "ortools/sat/timetable.h"
#include "ortools/sat/util.h"
#include "ortools/util/scheduling.h"
#include "ortools/util/sort.h"
#include "ortools/util/strong_integers.h"
namespace operations_research {
namespace sat {
void AddDisjunctive(const std::vector<Literal>& enforcement_literals,
const std::vector<IntervalVariable>& intervals,
Model* model) {
// Depending on the parameters, create all pair of conditional precedences.
// TODO(user): create them dynamically instead?
const auto& params = *model->GetOrCreate<SatParameters>();
if (intervals.size() <=
params.max_size_to_create_precedence_literals_in_disjunctive() &&
params.use_strong_propagation_in_disjunctive() &&
enforcement_literals.empty()) {
AddDisjunctiveWithBooleanPrecedencesOnly(intervals, model);
}
bool is_all_different = true;
IntervalsRepository* repository = model->GetOrCreate<IntervalsRepository>();
for (const IntervalVariable var : intervals) {
if (repository->IsOptional(var) || repository->MinSize(var) != 1 ||
repository->MaxSize(var) != 1) {
is_all_different = false;
break;
}
}
if (is_all_different) {
std::vector<AffineExpression> starts;
starts.reserve(intervals.size());
for (const IntervalVariable interval : intervals) {
starts.push_back(repository->Start(interval));
}
model->Add(AllDifferentOnBounds(enforcement_literals, starts));
return;
}
auto* watcher = model->GetOrCreate<GenericLiteralWatcher>();
if (intervals.size() > 2 && params.use_combined_no_overlap() &&
enforcement_literals.empty()) {
model->GetOrCreate<CombinedDisjunctive<true>>()->AddNoOverlap(intervals);
model->GetOrCreate<CombinedDisjunctive<false>>()->AddNoOverlap(intervals);
return;
}
SchedulingConstraintHelper* helper = repository->GetOrCreateHelper(
enforcement_literals, intervals, /*register_as_disjunctive_helper=*/true);
// Experiments to use the timetable only to propagate the disjunctive.
if (/*DISABLES_CODE*/ (false && enforcement_literals.empty())) {
const AffineExpression one(IntegerValue(1));
std::vector<AffineExpression> demands(intervals.size(), one);
SchedulingDemandHelper* demands_helper =
repository->GetOrCreateDemandHelper(helper, demands);
TimeTablingPerTask* timetable =
new TimeTablingPerTask(one, helper, demands_helper, model);
timetable->RegisterWith(watcher);
model->TakeOwnership(timetable);
return;
}
if (intervals.size() == 2) {
DisjunctiveWithTwoItems* propagator = new DisjunctiveWithTwoItems(helper);
propagator->RegisterWith(watcher);
model->TakeOwnership(propagator);
} else {
// We decided to create the propagators in this particular order, but it
// shouldn't matter much because of the different priorities used.
if (!params.use_strong_propagation_in_disjunctive()) {
// This one will not propagate anything if we added all precedence
// literals since the linear propagator will already do that in that case.
DisjunctiveSimplePrecedences* simple_precedences =
new DisjunctiveSimplePrecedences(helper, model);
const int id = simple_precedences->RegisterWith(watcher);
watcher->SetPropagatorPriority(id, 1);
model->TakeOwnership(simple_precedences);
}
{
// Only one direction is needed by this one.
DisjunctiveOverloadChecker* overload_checker =
new DisjunctiveOverloadChecker(helper, model);
const int id = overload_checker->RegisterWith(watcher);
watcher->SetPropagatorPriority(id, 1);
model->TakeOwnership(overload_checker);
}
for (const bool time_direction : {true, false}) {
DisjunctiveDetectablePrecedences* detectable_precedences =
new DisjunctiveDetectablePrecedences(time_direction, helper, model);
const int id = detectable_precedences->RegisterWith(watcher);
watcher->SetPropagatorPriority(id, 2);
model->TakeOwnership(detectable_precedences);
}
for (const bool time_direction : {true, false}) {
DisjunctiveNotLast* not_last =
new DisjunctiveNotLast(time_direction, helper, model);
const int id = not_last->RegisterWith(watcher);
watcher->SetPropagatorPriority(id, 3);
model->TakeOwnership(not_last);
}
for (const bool time_direction : {true, false}) {
DisjunctiveEdgeFinding* edge_finding =
new DisjunctiveEdgeFinding(time_direction, helper, model);
const int id = edge_finding->RegisterWith(watcher);
watcher->SetPropagatorPriority(id, 4);
model->TakeOwnership(edge_finding);
}
}
// Note that we keep this one even when there is just two intervals. This is
// because it might push a variable that is after both of the intervals
// using the fact that they are in disjunction.
if (params.use_precedences_in_disjunctive_constraint() &&
!params.use_combined_no_overlap()) {
// Lets try to exploit linear3 too.
model->GetOrCreate<LinearPropagator>()->SetPushAffineUbForBinaryRelation();
for (const bool time_direction : {true, false}) {
DisjunctivePrecedences* precedences =
new DisjunctivePrecedences(time_direction, helper, model);
const int id = precedences->RegisterWith(watcher);
watcher->SetPropagatorPriority(id, 5);
model->TakeOwnership(precedences);
}
}
}
void AddDisjunctiveWithBooleanPrecedencesOnly(
absl::Span<const IntervalVariable> intervals, Model* model) {
auto* repo = model->GetOrCreate<IntervalsRepository>();
for (int i = 0; i < intervals.size(); ++i) {
for (int j = i + 1; j < intervals.size(); ++j) {
repo->CreateDisjunctivePrecedenceLiteral(intervals[i], intervals[j]);
}
}
}
void TaskSet::AddEntry(const Entry& e) {
int j = sorted_tasks_.size();
sorted_tasks_.push_back(e);
while (j > 0 && sorted_tasks_[j - 1].start_min > e.start_min) {
sorted_tasks_[j] = sorted_tasks_[j - 1];
--j;
}
sorted_tasks_[j] = e;
DCHECK(std::is_sorted(sorted_tasks_.begin(), sorted_tasks_.end()));
// If the task is added after optimized_restart_, we know that we don't need
// to scan the task before optimized_restart_ in the next ComputeEndMin().
if (j <= optimized_restart_) optimized_restart_ = 0;
}
void TaskSet::AddShiftedStartMinEntry(const SchedulingConstraintHelper& helper,
int t) {
const IntegerValue dmin = helper.SizeMin(t);
AddEntry({t, std::max(helper.StartMin(t), helper.EndMin(t) - dmin), dmin});
}
void TaskSet::NotifyEntryIsNowLastIfPresent(const Entry& e) {
const int size = sorted_tasks_.size();
for (int i = 0;; ++i) {
if (i == size) return;
if (sorted_tasks_[i].task == e.task) {
for (int j = i; j + 1 < size; ++j) {
sorted_tasks_[j] = sorted_tasks_[j + 1];
}
sorted_tasks_.pop_back();
break;
}
}
optimized_restart_ = sorted_tasks_.size();
sorted_tasks_.push_back(e);
DCHECK(std::is_sorted(sorted_tasks_.begin(), sorted_tasks_.end()));
}
IntegerValue TaskSet::ComputeEndMin() const {
DCHECK(std::is_sorted(sorted_tasks_.begin(), sorted_tasks_.end()));
const int size = sorted_tasks_.size();
IntegerValue end_min = kMinIntegerValue;
for (int i = optimized_restart_; i < size; ++i) {
const Entry& e = sorted_tasks_[i];
if (e.start_min >= end_min) {
optimized_restart_ = i;
end_min = e.start_min + e.size_min;
} else {
end_min += e.size_min;
}
}
return end_min;
}
IntegerValue TaskSet::ComputeEndMin(int task_to_ignore,
int* critical_index) const {
// The order in which we process tasks with the same start-min doesn't matter.
DCHECK(std::is_sorted(sorted_tasks_.begin(), sorted_tasks_.end()));
bool ignored = false;
const int size = sorted_tasks_.size();
IntegerValue end_min = kMinIntegerValue;
// If the ignored task is last and was the start of the critical block, then
// we need to reset optimized_restart_.
if (optimized_restart_ + 1 == size &&
sorted_tasks_[optimized_restart_].task == task_to_ignore) {
optimized_restart_ = 0;
}
for (int i = optimized_restart_; i < size; ++i) {
const Entry& e = sorted_tasks_[i];
if (e.task == task_to_ignore) {
ignored = true;
continue;
}
if (e.start_min >= end_min) {
*critical_index = i;
if (!ignored) optimized_restart_ = i;
end_min = e.start_min + e.size_min;
} else {
end_min += e.size_min;
}
}
return end_min;
}
bool DisjunctiveWithTwoItems::Propagate() {
DCHECK_EQ(helper_->NumTasks(), 2);
if (!helper_->IsEnforced()) return true;
if (!helper_->SynchronizeAndSetTimeDirection(true)) return false;
// We can't propagate anything if one of the interval is absent for sure.
if (helper_->IsAbsent(0) || helper_->IsAbsent(1)) return true;
// We can't propagate anything for two intervals if neither are present.
if (!helper_->IsPresent(0) && !helper_->IsPresent(0)) return true;
// Note that this propagation also take care of the "overload checker" part.
// It also propagates as much as possible, even in the presence of task with
// variable sizes.
//
// TODO(user): For optional interval whose presence in unknown and without
// optional variable, the end-min may not be propagated to at least (start_min
// + size_min). Consider that into the computation so we may decide the
// interval forced absence? Same for the start-max.
int task_before = 0;
int task_after = 1;
const bool task_0_before_task_1 = helper_->TaskIsBeforeOrIsOverlapping(0, 1);
const bool task_1_before_task_0 = helper_->TaskIsBeforeOrIsOverlapping(1, 0);
if (task_0_before_task_1 && task_1_before_task_0 &&
helper_->IsPresent(task_before) && helper_->IsPresent(task_after)) {
helper_->ResetReason();
helper_->AddPresenceReason(task_before);
helper_->AddPresenceReason(task_after);
helper_->AddReasonForBeingBeforeAssumingNoOverlap(task_before, task_after);
helper_->AddReasonForBeingBeforeAssumingNoOverlap(task_after, task_before);
return helper_->ReportConflict();
}
if (task_0_before_task_1) {
// Task 0 must be before task 1.
} else if (task_1_before_task_0) {
// Task 1 must be before task 0.
std::swap(task_before, task_after);
} else {
return true;
}
helper_->ResetReason();
helper_->AddReasonForBeingBeforeAssumingNoOverlap(task_before, task_after);
if (!helper_->PushTaskOrderWhenPresent(task_before, task_after)) {
return false;
}
return true;
}
int DisjunctiveWithTwoItems::RegisterWith(GenericLiteralWatcher* watcher) {
const int id = watcher->Register(this);
helper_->WatchAllTasks(id);
watcher->NotifyThatPropagatorMayNotReachFixedPointInOnePass(id);
return id;
}
template <bool time_direction>
CombinedDisjunctive<time_direction>::CombinedDisjunctive(Model* model)
: helper_(model->GetOrCreate<IntervalsRepository>()->GetOrCreateHelper(
/*enforcement_literals=*/{},
model->GetOrCreate<IntervalsRepository>()->AllIntervals())) {
task_to_disjunctives_.resize(helper_->NumTasks());
auto* watcher = model->GetOrCreate<GenericLiteralWatcher>();
const int id = watcher->Register(this);
helper_->WatchAllTasks(id);
watcher->NotifyThatPropagatorMayNotReachFixedPointInOnePass(id);
}
template <bool time_direction>
void CombinedDisjunctive<time_direction>::AddNoOverlap(
absl::Span<const IntervalVariable> vars) {
const int index = task_sets_.size();
task_sets_.emplace_back(task_set_storage_.emplace_back());
end_mins_.push_back(kMinIntegerValue);
for (const IntervalVariable var : vars) {
task_to_disjunctives_[var.value()].push_back(index);
}
}
template <bool time_direction>
bool CombinedDisjunctive<time_direction>::Propagate() {
if (!helper_->SynchronizeAndSetTimeDirection(time_direction)) return false;
const auto& task_by_increasing_end_min = helper_->TaskByIncreasingEndMin();
const auto& task_by_negated_start_max =
helper_->TaskByIncreasingNegatedStartMax();
for (auto& task_set : task_sets_) task_set.Clear();
end_mins_.assign(end_mins_.size(), kMinIntegerValue);
IntegerValue max_of_end_min = kMinIntegerValue;
const int num_tasks = helper_->NumTasks();
task_is_added_.assign(num_tasks, false);
int queue_index = num_tasks - 1;
for (const auto task_time : task_by_increasing_end_min) {
const int t = task_time.task_index;
const IntegerValue end_min = task_time.time;
if (helper_->IsAbsent(t)) continue;
// Update all task sets.
while (queue_index >= 0) {
const auto to_insert = task_by_negated_start_max[queue_index];
const int task_index = to_insert.task_index;
const IntegerValue start_max = -to_insert.time;
if (end_min <= start_max) break;
if (helper_->IsPresent(task_index)) {
task_is_added_[task_index] = true;
const IntegerValue shifted_smin = helper_->ShiftedStartMin(task_index);
const IntegerValue size_min = helper_->SizeMin(task_index);
for (const int d_index : task_to_disjunctives_[task_index]) {
// TODO(user): AddEntry() and ComputeEndMin() could be combined.
task_sets_[d_index].AddEntry({task_index, shifted_smin, size_min});
end_mins_[d_index] = task_sets_[d_index].ComputeEndMin();
max_of_end_min = std::max(max_of_end_min, end_mins_[d_index]);
}
}
--queue_index;
}
// Find out amongst the disjunctives in which t appear, the one with the
// largest end_min, ignoring t itself. This will be the new start min for t.
IntegerValue new_start_min = helper_->StartMin(t);
if (new_start_min >= max_of_end_min) continue;
int best_critical_index = 0;
int best_d_index = -1;
if (task_is_added_[t]) {
for (const int d_index : task_to_disjunctives_[t]) {
if (new_start_min >= end_mins_[d_index]) continue;
int critical_index = 0;
const IntegerValue end_min_of_critical_tasks =
task_sets_[d_index].ComputeEndMin(/*task_to_ignore=*/t,
&critical_index);
DCHECK_LE(end_min_of_critical_tasks, max_of_end_min);
if (end_min_of_critical_tasks > new_start_min) {
new_start_min = end_min_of_critical_tasks;
best_d_index = d_index;
best_critical_index = critical_index;
}
}
} else {
// If the task t was not added, then there is no task to ignore and
// end_mins_[d_index] is up to date.
for (const int d_index : task_to_disjunctives_[t]) {
if (end_mins_[d_index] > new_start_min) {
new_start_min = end_mins_[d_index];
best_d_index = d_index;
}
}
if (best_d_index != -1) {
const IntegerValue end_min_of_critical_tasks =
task_sets_[best_d_index].ComputeEndMin(/*task_to_ignore=*/t,
&best_critical_index);
CHECK_EQ(end_min_of_critical_tasks, new_start_min);
}
}
// Do we push something?
if (best_d_index == -1) continue;
// Same reason as DisjunctiveDetectablePrecedences.
// TODO(user): Maybe factor out the code? It does require a function with a
// lot of arguments though.
helper_->ResetReason();
const absl::Span<const TaskSet::Entry> sorted_tasks =
task_sets_[best_d_index].SortedTasks();
const IntegerValue window_start =
sorted_tasks[best_critical_index].start_min;
for (int i = best_critical_index; i < sorted_tasks.size(); ++i) {
const int ct = sorted_tasks[i].task;
if (ct == t) continue;
helper_->AddPresenceReason(ct);
helper_->AddEnergyAfterReason(ct, sorted_tasks[i].size_min, window_start);
helper_->AddStartMaxReason(ct, end_min - 1);
}
helper_->AddEndMinReason(t, end_min);
if (!helper_->IncreaseStartMin(t, new_start_min)) {
return false;
}
// We need to reorder t inside task_set_. Note that if t is in the set,
// it means that the task is present and that IncreaseStartMin() did push
// its start (by opposition to an optional interval where the push might
// not happen if its start is not optional).
if (task_is_added_[t]) {
const IntegerValue shifted_smin = helper_->ShiftedStartMin(t);
const IntegerValue size_min = helper_->SizeMin(t);
for (const int d_index : task_to_disjunctives_[t]) {
// TODO(user): Refactor the code to use the same algo as in
// DisjunctiveDetectablePrecedences, it is superior and do not need
// this function.
task_sets_[d_index].NotifyEntryIsNowLastIfPresent(
{t, shifted_smin, size_min});
end_mins_[d_index] = task_sets_[d_index].ComputeEndMin();
max_of_end_min = std::max(max_of_end_min, end_mins_[d_index]);
}
}
}
return true;
}
bool DisjunctiveOverloadChecker::Propagate() {
if (!helper_->IsEnforced()) return true;
stats_.OnPropagate();
if (!helper_->SynchronizeAndSetTimeDirection(/*is_forward=*/true)) {
++stats_.num_conflicts;
return false;
}
absl::Span<TaskTime> window_span =
absl::MakeSpan(helper_->GetScratchTaskTimeVector1());
// We use this to detect precedence between task that must cause a push.
TaskTime task_with_max_end_min = {0, kMinIntegerValue};
// We will process the task by increasing shifted_end_max, thus consuming task
// from the end of that vector.
absl::Span<const CachedTaskBounds>
task_by_increasing_negated_shifted_end_max =
helper_->TaskByIncreasingNegatedShiftedEndMax();
// Split problem into independent part.
//
// Many propagators in this file use the same approach, we start by processing
// the task by increasing shifted start-min, packing everything to the left.
// We then process each "independent" set of task separately. A task is
// independent from the one before it, if its start-min wasn't pushed.
//
// This way, we get one or more window [window_start, window_end] so that for
// all task in the window, [start_min, end_min] is inside the window, and the
// end min of any set of task to the left is <= window_start, and the
// start_min of any task to the right is >= window_end.
// We keep the best end_min for present task only and present task plus at
// most a single optional task.
IntegerValue end_min_of_present = kMinIntegerValue;
IntegerValue end_min_with_one_optional = kMinIntegerValue;
IntegerValue relevant_end;
int window_size = 0;
int relevant_size = 0;
TaskTime* const window = window_span.data();
for (const auto [task, presence_lit, start_min] :
helper_->TaskByIncreasingShiftedStartMin()) {
if (helper_->IsAbsent(presence_lit)) continue;
// Nothing to do with overload checking, but almost free to do that here.
const IntegerValue size_min = helper_->SizeMin(task);
const IntegerValue end_min = start_min + size_min;
const IntegerValue start_max = helper_->StartMax(task);
if (start_max < task_with_max_end_min.time &&
helper_->IsPresent(presence_lit) && size_min > 0) {
// We have a detectable precedence that must cause a push.
//
// Remarks: If we added all precedence literals + linear relation, this
// propagation would have been done by the linear propagator, but if we
// didn't add such relations yet, it is beneficial to detect that here!
//
// TODO(user): Actually, we just inferred a "not last" so we could check
// for relevant_size > 2 potential propagation?
//
// Note that the DisjunctiveSimplePrecedences propagators will also
// detects such precedences between two tasks.
const int to_push = task_with_max_end_min.task_index;
helper_->ResetReason();
helper_->AddReasonForBeingBeforeAssumingNoOverlap(task, to_push);
if (!helper_->PushTaskOrderWhenPresent(task, to_push)) {
++stats_.num_conflicts;
return false;
}
// TODO(user): Shall we keep propagating? we know the prefix didn't
// change, so we could be faster here. On another hand, it might be
// better to propagate all the linear constraints before returning
// here.
++stats_.num_propagations;
stats_.EndWithoutConflicts();
return true;
}
// Note that we need to do that AFTER the block above.
if (end_min > task_with_max_end_min.time) {
task_with_max_end_min = {task, end_min};
}
// Extend window.
const IntegerValue old_value = end_min_with_one_optional;
if (start_min < end_min_with_one_optional) {
window[window_size++] = {task, start_min};
if (helper_->IsPresent(presence_lit)) {
end_min_of_present =
std::max(start_min + size_min, end_min_of_present + size_min);
end_min_with_one_optional += size_min;
} else {
if (end_min_of_present == kMinIntegerValue) {
// only optional:
end_min_with_one_optional =
std::max(end_min_with_one_optional, start_min + size_min);
} else {
end_min_with_one_optional =
std::max(end_min_with_one_optional,
std::max(end_min_of_present, start_min) + size_min);
}
}
if (old_value > start_max) {
relevant_size = window_size;
relevant_end = end_min_with_one_optional;
}
continue;
}
// Process current window.
// We don't need to process the end of the window (after relevant_size)
// because these interval can be greedily assembled in a feasible solution.
if (relevant_size > 0 &&
!PropagateSubwindow(window_span.subspan(0, relevant_size), relevant_end,
&task_by_increasing_negated_shifted_end_max)) {
++stats_.num_conflicts;
return false;
}
// Subwindow propagation might have propagated that the
// task_with_max_end_min must be absent.
if (helper_->IsAbsent(task_with_max_end_min.task_index)) {
task_with_max_end_min = {0, kMinIntegerValue};
}
// Start of the next window.
window_size = 0;
window[window_size++] = {task, start_min};
if (helper_->IsPresent(presence_lit)) {
end_min_of_present = start_min + size_min;
end_min_with_one_optional = end_min_of_present;
} else {
end_min_of_present = kMinIntegerValue;
end_min_with_one_optional = start_min + size_min;
}
relevant_size = 0;
}
// Process last window.
if (relevant_size > 0 &&
!PropagateSubwindow(window_span.subspan(0, relevant_size), relevant_end,
&task_by_increasing_negated_shifted_end_max)) {
++stats_.num_conflicts;
return false;
}
if (DEBUG_MODE) {
// This test that our "subwindow" logic is sound and we don't miss any
// conflict or propagation by splitting the intervals like this.
//
// TODO(user): I think we can come up with corner case where pushing a task
// absence forces another one to be present, which might create more
// propagation. This is the same reason why we might not reach a fixed point
// in one go. However this should be rare and that piece of code allowed me
// to fix many bug. So I left it as is, we can revisit if we starts to see
// crashes on our tests.
window_size = 0;
task_by_increasing_negated_shifted_end_max =
helper_->TaskByIncreasingNegatedShiftedEndMax();
for (const auto [task, presence_lit, start_min] :
helper_->TaskByIncreasingShiftedStartMin()) {
if (helper_->IsAbsent(presence_lit)) continue;
window[window_size++] = {task, start_min};
}
const int64_t saved = helper_->PropagationTimestamp();
CHECK(PropagateSubwindow(window_span.subspan(0, window_size),
kMaxIntegerValue,
&task_by_increasing_negated_shifted_end_max));
CHECK_EQ(saved, helper_->PropagationTimestamp());
}
stats_.EndWithoutConflicts();
return true;
}
// TODO(user): Improve the Overload Checker using delayed insertion.
// We insert events at the cost of O(log n) per insertion, and this is where
// the algorithm spends most of its time, thus it is worth improving.
// We can insert an arbitrary set of tasks at the cost of O(n) for the whole
// set. This is useless for the overload checker as is since we need to check
// overload after every insertion, but we could use an upper bound of the
// theta envelope to save us from checking the actual value.
bool DisjunctiveOverloadChecker::PropagateSubwindow(
absl::Span<TaskTime> sub_window, IntegerValue global_window_end,
absl::Span<const CachedTaskBounds>*
task_by_increasing_negated_shifted_end_max) {
// Set up theta tree.
TaskTime* const window = sub_window.data();
int num_events = 0;
for (int i = 0; i < sub_window.size(); ++i) {
// No point adding a task if its end_max is too large.
const TaskTime& task_time = window[i];
const int task = task_time.task_index;
// We use the shifted end-max which might be < EndMax().
const IntegerValue end_max = helper_->ShiftedEndMax(task);
if (end_max < global_window_end) {
window[num_events] = task_time;
task_to_event_[task] = num_events;
++num_events;
}
}
if (num_events <= 1) return true;
theta_tree_.Reset(num_events);
// Introduce events by increasing end_max, check for overloads.
while (!task_by_increasing_negated_shifted_end_max->empty()) {
const auto [current_task, presence_lit, minus_shifted_end_max] =
task_by_increasing_negated_shifted_end_max->back();
const IntegerValue current_end = -minus_shifted_end_max;
DCHECK_EQ(current_end, helper_->ShiftedEndMax(current_task));
if (current_end >= global_window_end) return true; // go to next window.
task_by_increasing_negated_shifted_end_max->remove_suffix(1); // consume.
// Ignore task not part of that window.
// Note that we never clear task_to_event_, so it might contains garbage
// for the values that we didn't set above. However, we can easily check
// if task_to_event_[current_task] point to an element that we set above.
// This is a bit faster than clearing task_to_event_ on exit.
const int current_event = task_to_event_[current_task];
if (current_event < 0 || current_event >= num_events) continue;
if (window[current_event].task_index != current_task) continue;
// We filtered absent task while constructing the subwindow, but it is
// possible that as we propagate task absence below, other task also become
// absent (if they share the same presence Boolean).
if (helper_->IsAbsent(presence_lit)) continue;
DCHECK_NE(task_to_event_[current_task], -1);
{
const IntegerValue energy_min = helper_->SizeMin(current_task);
if (helper_->IsPresent(presence_lit)) {
// TODO(user): Add max energy deduction for variable
// sizes by putting the energy_max here and modifying the code
// dealing with the optional envelope greater than current_end below.
theta_tree_.AddOrUpdateEvent(current_event, window[current_event].time,
energy_min, energy_min);
} else {
theta_tree_.AddOrUpdateOptionalEvent(
current_event, window[current_event].time, energy_min);
}
}
if (theta_tree_.GetEnvelope() > current_end) {
// Explain failure with tasks in critical interval.
helper_->ResetReason();
const int critical_event =
theta_tree_.GetMaxEventWithEnvelopeGreaterThan(current_end);
const IntegerValue window_start = window[critical_event].time;
const IntegerValue window_end =
theta_tree_.GetEnvelopeOf(critical_event) - 1;
for (int event = critical_event; event < num_events; event++) {
const IntegerValue energy_min = theta_tree_.EnergyMin(event);
if (energy_min > 0) {
const int task = window[event].task_index;
helper_->AddPresenceReason(task);
helper_->AddEnergyAfterReason(task, energy_min, window_start);
helper_->AddShiftedEndMaxReason(task, window_end);
}
}
return helper_->ReportConflict();
}
// Exclude all optional tasks that would overload an interval ending here.
while (theta_tree_.GetOptionalEnvelope() > current_end) {
// Explain exclusion with tasks present in the critical interval.
// TODO(user): This could be done lazily, like most of the loop to
// compute the reasons in this file.
helper_->ResetReason();
int critical_event;
int optional_event;
IntegerValue available_energy;
theta_tree_.GetEventsWithOptionalEnvelopeGreaterThan(
current_end, &critical_event, &optional_event, &available_energy);
const int optional_task = window[optional_event].task_index;
// If tasks shares the same presence literal, it is possible that we
// already pushed this task absence.
if (!helper_->IsAbsent(optional_task)) {
const IntegerValue optional_size_min = helper_->SizeMin(optional_task);
const IntegerValue window_start = window[critical_event].time;
const IntegerValue window_end =
current_end + optional_size_min - available_energy - 1;
for (int event = critical_event; event < num_events; event++) {
const IntegerValue energy_min = theta_tree_.EnergyMin(event);
if (energy_min > 0) {
const int task = window[event].task_index;
helper_->AddPresenceReason(task);
helper_->AddEnergyAfterReason(task, energy_min, window_start);
helper_->AddShiftedEndMaxReason(task, window_end);
}
}
helper_->AddEnergyAfterReason(optional_task, optional_size_min,
window_start);
helper_->AddShiftedEndMaxReason(optional_task, window_end);
++stats_.num_propagations;
if (!helper_->PushTaskAbsence(optional_task)) return false;
}
theta_tree_.RemoveEvent(optional_event);
}
}
return true;
}
int DisjunctiveOverloadChecker::RegisterWith(GenericLiteralWatcher* watcher) {
// This propagator should mostly reach the fix point in one pass, except if
// pushing a task absence make another task present... So we still prefer to
// re-run it as it is relatively fast.
const int id = watcher->Register(this);
helper_->SetTimeDirection(/*is_forward=*/true);
watcher->NotifyThatPropagatorMayNotReachFixedPointInOnePass(id);
helper_->WatchAllTasks(id);
return id;
}
int DisjunctiveSimplePrecedences::RegisterWith(GenericLiteralWatcher* watcher) {
const int id = watcher->Register(this);
helper_->WatchAllTasks(id);
watcher->NotifyThatPropagatorMayNotReachFixedPointInOnePass(id);
return id;
}
bool DisjunctiveSimplePrecedences::Propagate() {
if (!helper_->IsEnforced()) return true;
stats_.OnPropagate();
const bool current_direction = helper_->CurrentTimeIsForward();
for (const bool direction : {current_direction, !current_direction}) {
if (!helper_->SynchronizeAndSetTimeDirection(direction)) {
++stats_.num_conflicts;
return false;
}
if (!PropagateOneDirection()) {
++stats_.num_conflicts;
return false;
}
}
stats_.EndWithoutConflicts();
return true;
}
bool DisjunctiveSimplePrecedences::Push(TaskTime before, int t) {
const int t_before = before.task_index;
DCHECK_NE(t_before, t);
helper_->ResetReason();
helper_->AddReasonForBeingBeforeAssumingNoOverlap(t_before, t);
if (!helper_->PushTaskOrderWhenPresent(t_before, t)) return false;
++stats_.num_propagations;
return true;
}
bool DisjunctiveSimplePrecedences::PropagateOneDirection() {
// We will loop in a decreasing way here.
// And add tasks that are present to the task_set_.
absl::Span<const TaskTime> task_by_negated_start_max =
helper_->TaskByIncreasingNegatedStartMax();
// We just keep amongst all the task before current_end_min, the one with the
// highesh end-min.
TaskTime best_task_before = {-1, kMinIntegerValue};
// We will loop in an increasing way here and consume task from beginning.
absl::Span<const TaskTime> task_by_increasing_end_min =
helper_->TaskByIncreasingEndMin();
for (; !task_by_increasing_end_min.empty();) {
// Skip absent task.
if (helper_->IsAbsent(task_by_increasing_end_min.front().task_index)) {
task_by_increasing_end_min.remove_prefix(1);
continue;
}
// Consider all task with a start_max < current_end_min.
int blocking_task = -1;
IntegerValue blocking_start_max;
IntegerValue current_end_min = task_by_increasing_end_min.front().time;
for (; true; task_by_negated_start_max.remove_suffix(1)) {
if (task_by_negated_start_max.empty()) {
// Small optim: this allows to process all remaining task rather than
// looping around are retesting this for all remaining tasks.
current_end_min = kMaxIntegerValue;
break;
}
const auto [t, negated_start_max] = task_by_negated_start_max.back();
const IntegerValue start_max = -negated_start_max;
if (current_end_min <= start_max) break;
if (!helper_->IsPresent(t)) continue;
// If t has a mandatory part, and extend further than current_end_min
// then we can push it first. All tasks for which their push is delayed
// are necessarily after this "blocking task".
//
// This idea is introduced in "Linear-Time Filtering Algorithms for the
// Disjunctive Constraints" Hamed Fahimi, Claude-Guy Quimper.
const IntegerValue end_min = helper_->EndMin(t);
if (blocking_task == -1 && end_min >= current_end_min) {
DCHECK_LT(start_max, end_min) << " task should have mandatory part: "
<< helper_->TaskDebugString(t);
blocking_task = t;
blocking_start_max = start_max;
current_end_min = end_min;
} else if (blocking_task != -1 && blocking_start_max < end_min) {
// Conflict! the task is after the blocking_task but also before.
helper_->ResetReason();
helper_->AddPresenceReason(blocking_task);
helper_->AddPresenceReason(t);
helper_->AddReasonForBeingBeforeAssumingNoOverlap(blocking_task, t);
helper_->AddReasonForBeingBeforeAssumingNoOverlap(t, blocking_task);
return helper_->ReportConflict();
} else if (end_min > best_task_before.time) {
best_task_before = {t, end_min};
}
}
// If we have a blocking task. We need to propagate it first.
if (blocking_task != -1) {
DCHECK(!helper_->IsAbsent(blocking_task));
if (best_task_before.time > helper_->StartMin(blocking_task)) {
if (!Push(best_task_before, blocking_task)) return false;
}
// Update best_task_before.
//
// Note that we want the blocking task here as it is the only one
// guaranteed to be before all the task we push below. If we are not in a
// propagation loop, it should also be the best.
const IntegerValue end_min = helper_->EndMin(blocking_task);
best_task_before = {blocking_task, end_min};
}
// Lets propagate all task after best_task_before.
for (; !task_by_increasing_end_min.empty();
task_by_increasing_end_min.remove_prefix(1)) {
const auto [t, end_min] = task_by_increasing_end_min.front();
if (end_min > current_end_min) break;
if (t == blocking_task) continue; // Already done.
// Lets propagate current_task.
if (best_task_before.time > helper_->StartMin(t)) {
// Corner case if a previous push caused a subsequent task to be absent.
if (helper_->IsAbsent(t)) continue;
if (!Push(best_task_before, t)) return false;
}
}
}
return true;
}
bool DisjunctiveDetectablePrecedences::Propagate() {
if (!helper_->IsEnforced()) return true;
stats_.OnPropagate();
if (!helper_->SynchronizeAndSetTimeDirection(time_direction_)) {
++stats_.num_conflicts;
return false;
}
// Compute the "rank" of each task.
const auto by_shifted_smin = helper_->TaskByIncreasingShiftedStartMin();
int rank = -1;
IntegerValue window_end = kMinIntegerValue;
int* const ranks = ranks_.data();
for (const auto [task, presence_lit, start_min] : by_shifted_smin) {
if (!helper_->IsPresent(presence_lit)) {
ranks[task] = -1;
continue;
}
const IntegerValue size_min = helper_->SizeMin(task);
if (start_min < window_end) {
ranks[task] = rank;
window_end += size_min;
} else {
ranks[task] = ++rank;
window_end = start_min + size_min;
}
}
if (!PropagateWithRanks()) {
++stats_.num_conflicts;
return false;
}
stats_.EndWithoutConflicts();
return true;
}
// task_set_ contains all the tasks that must be executed before t. They
// are in "detectable precedence" because their start_max is smaller than
// the end-min of t like so:
// [(the task t)
// (a task in task_set_)]
// From there, we deduce that the start-min of t is greater or equal to
// the end-min of the critical tasks.
//
// Note that this works as well when IsPresent(t) is false.
bool DisjunctiveDetectablePrecedences::Push(IntegerValue task_set_end_min,
int t, TaskSet& task_set) {
const int critical_index = task_set.GetCriticalIndex();
const absl::Span<const TaskSet::Entry> sorted_tasks = task_set.SortedTasks();
helper_->ResetReason();
// We need:
// - StartMax(ct) < EndMin(t) for the detectable precedence.
// - StartMin(ct) >= window_start for the value of task_set_end_min.
const IntegerValue end_min_if_present =
helper_->ShiftedStartMin(t) + helper_->SizeMin(t);
const IntegerValue window_start = sorted_tasks[critical_index].start_min;
IntegerValue min_slack = kMaxIntegerValue;
bool all_already_before = true;
IntegerValue energy_of_task_before = 0;
for (int i = critical_index; i < sorted_tasks.size(); ++i) {
const int ct = sorted_tasks[i].task;
DCHECK_NE(ct, t);
helper_->AddPresenceReason(ct);
// Heuristic, if some tasks are known to be after the first one,
// we just add the min-size as a reason.
//
// TODO(user): ideally we don't want to do that if we don't have a level
// zero precedence...
if (i > critical_index && helper_->GetCurrentMinDistanceBetweenTasks(
sorted_tasks[critical_index].task, ct) >= 0) {
helper_->AddReasonForBeingBeforeAssumingNoOverlap(
sorted_tasks[critical_index].task, ct);
helper_->AddSizeMinReason(ct);
} else {
helper_->AddEnergyAfterReason(ct, sorted_tasks[i].size_min, window_start);
}
// We only need the reason for being before if we don't already have
// a static precedence between the tasks.
const IntegerValue dist = helper_->GetCurrentMinDistanceBetweenTasks(ct, t);
if (dist >= 0) {
helper_->AddReasonForBeingBeforeAssumingNoOverlap(ct, t);
energy_of_task_before += sorted_tasks[i].size_min;
min_slack = std::min(min_slack, dist);
// TODO(user): The reason in AddReasonForBeingBeforeAssumingNoOverlap()
// only account for dist == 0 !! If we want to use a stronger strictly
// positive distance, we actually need to explain it. Fix this.
min_slack = 0;
} else {
all_already_before = false;
helper_->AddStartMaxReason(ct, end_min_if_present - 1);
}
}
// We only need the end-min of t if not all the task are already known
// to be before.
IntegerValue new_start_min = task_set_end_min;
if (all_already_before) {
// We can actually push further!
// And we don't need other reason except the precedences.
new_start_min += min_slack;
} else {
helper_->AddEndMinReason(t, end_min_if_present);
}
// In some situation, we can push the task further.
// TODO(user): We can also reduce the reason in this case.
if (min_slack != kMaxIntegerValue &&
window_start + energy_of_task_before + min_slack > new_start_min) {
new_start_min = window_start + energy_of_task_before + min_slack;
}
// Process detected precedence.
if (helper_->CurrentDecisionLevel() == 0 && helper_->IsPresent(t)) {
for (int i = critical_index; i < sorted_tasks.size(); ++i) {
if (!helper_->NotifyLevelZeroPrecedence(sorted_tasks[i].task, t)) {
return false;
}
}
}
// This augment the start-min of t. Note that t is not in task set
// yet, so we will use this updated start if we ever add it there.
++stats_.num_propagations;
if (!helper_->IncreaseStartMin(t, new_start_min)) {
return false;
}
return true;
}
bool DisjunctiveDetectablePrecedences::PropagateWithRanks() {
// We will "consume" tasks from here.
absl::Span<const TaskTime> task_by_increasing_end_min =
helper_->TaskByIncreasingEndMin();
absl::Span<const TaskTime> task_by_negated_start_max =
helper_->TaskByIncreasingNegatedStartMax();
// We will stop using ranks as soon as we propagated something. This allow to
// be sure this propagate as much as possible in a single pass and seems to
// help slightly.
int highest_rank = 0;
bool some_propagation = false;
// Invariant: need_update is false implies that task_set_end_min is equal to
// task_set.ComputeEndMin().
//
// TODO(user): Maybe it is just faster to merge ComputeEndMin() with
// AddEntry().
TaskSet task_set(helper_->GetScratchTaskSet());
to_add_.clear();
IntegerValue task_set_end_min = kMinIntegerValue;
for (; !task_by_increasing_end_min.empty();) {
// Consider all task with a start_max < current_end_min.
int blocking_task = -1;
IntegerValue blocking_start_max;
IntegerValue current_end_min = task_by_increasing_end_min.front().time;
for (; true; task_by_negated_start_max.remove_suffix(1)) {
if (task_by_negated_start_max.empty()) {
// Small optim: this allows to process all remaining task rather than
// looping around are retesting this for all remaining tasks.
current_end_min = kMaxIntegerValue;
break;
}
const auto [t, negated_start_max] = task_by_negated_start_max.back();
const IntegerValue start_max = -negated_start_max;
if (current_end_min <= start_max) break;
// If the task is not present, its rank will be -1.
const int rank = ranks_[t];
if (rank < highest_rank) continue;
DCHECK(helper_->IsPresent(t));
// If t has a mandatory part, and extend further than current_end_min
// then we can push it first. All tasks for which their push is delayed
// are necessarily after this "blocking task".
//
// This idea is introduced in "Linear-Time Filtering Algorithms for the
// Disjunctive Constraints" Hamed Fahimi, Claude-Guy Quimper.
const IntegerValue end_min = helper_->EndMin(t);
if (blocking_task == -1 && end_min >= current_end_min) {
DCHECK_LT(start_max, end_min) << " task should have mandatory part: "
<< helper_->TaskDebugString(t);
blocking_task = t;
blocking_start_max = start_max;
current_end_min = end_min;
} else if (blocking_task != -1 && blocking_start_max < end_min) {
// Conflict! the task is after the blocking_task but also before.
helper_->ResetReason();
helper_->AddPresenceReason(blocking_task);
helper_->AddPresenceReason(t);
helper_->AddReasonForBeingBeforeAssumingNoOverlap(blocking_task, t);
helper_->AddReasonForBeingBeforeAssumingNoOverlap(t, blocking_task);
return helper_->ReportConflict();
} else {
if (!some_propagation && rank > highest_rank) {
to_add_.clear();
task_set.Clear();
highest_rank = rank;
}
to_add_.push_back(t);
}
}
// If we have a blocking task. We need to propagate it first.
if (blocking_task != -1) {
DCHECK(!helper_->IsAbsent(blocking_task));
if (!to_add_.empty()) {
for (const int t : to_add_) {
task_set.AddShiftedStartMinEntry(*helper_, t);
}
to_add_.clear();
task_set_end_min = task_set.ComputeEndMin();
}
if (task_set_end_min > helper_->StartMin(blocking_task)) {
some_propagation = true;
if (!Push(task_set_end_min, blocking_task, task_set)) return false;
}
// This propagators assumes that every push is reflected for its
// correctness.
if (helper_->InPropagationLoop()) return true;
// Insert the blocking_task. Note that because we just pushed it,
// it will be last in task_set_ and also the only reason used to push
// any of the subsequent tasks below. In particular, the reason will be
// valid even though task_set might contains tasks with a start_max
// greater or equal to the end_min of the task we push.
if (!some_propagation && ranks_[blocking_task] > highest_rank) {
to_add_.clear();
task_set.Clear();
highest_rank = ranks_[blocking_task];
}
to_add_.push_back(blocking_task);
}
// Lets propagate all task with end_min <= current_end_min that are also
// after all the task in task_set_.
for (; !task_by_increasing_end_min.empty();
task_by_increasing_end_min.remove_prefix(1)) {
const auto [t, end_min] = task_by_increasing_end_min.front();
if (end_min > current_end_min) break;
if (t == blocking_task) continue; // Already done.
if (!to_add_.empty()) {
for (const int t : to_add_) {
task_set.AddShiftedStartMinEntry(*helper_, t);
}
to_add_.clear();
task_set_end_min = task_set.ComputeEndMin();
}
// Lets propagate current_task.
if (task_set_end_min > helper_->StartMin(t)) {
// Corner case if a previous push caused a subsequent task to be absent.
if (helper_->IsAbsent(t)) continue;
some_propagation = true;
if (!Push(task_set_end_min, t, task_set)) return false;
}
}
}
return true;
}
int DisjunctiveDetectablePrecedences::RegisterWith(
GenericLiteralWatcher* watcher) {
const int id = watcher->Register(this);
helper_->SetTimeDirection(time_direction_);
helper_->WatchAllTasks(id);
watcher->NotifyThatPropagatorMayNotReachFixedPointInOnePass(id);
return id;
}
bool DisjunctivePrecedences::Propagate() {
if (!helper_->IsEnforced()) return true;
stats_.OnPropagate();
if (!helper_->SynchronizeAndSetTimeDirection(time_direction_)) {
++stats_.num_conflicts;
return false;
}
FixedCapacityVector<TaskTime>& window = helper_->GetScratchTaskTimeVector1();
// We only need to consider "critical" set of tasks given how we compute the
// min-offset in PropagateSubwindow().
IntegerValue window_end = kMinIntegerValue;
for (const auto [task, presence_lit, start_min] :
helper_->TaskByIncreasingShiftedStartMin()) {
if (!helper_->IsPresent(presence_lit)) continue;
if (start_min < window_end) {
window.push_back({task, start_min});
window_end += helper_->SizeMin(task);
continue;
}
if (window.size() > 1 && !PropagateSubwindow(absl::MakeSpan(window))) {
++stats_.num_conflicts;
return false;
}
// Start of the next window.
window.clear();
window.push_back({task, start_min});
window_end = start_min + helper_->SizeMin(task);
}
if (window.size() > 1 && !PropagateSubwindow(absl::MakeSpan(window))) {
++stats_.num_conflicts;
return false;
}
stats_.EndWithoutConflicts();
return true;
}
bool DisjunctivePrecedences::PropagateSubwindow(absl::Span<TaskTime> window) {
// This function can be slow, so count it in the dtime.
int64_t num_hash_lookup = 0;
auto cleanup = ::absl::MakeCleanup([&num_hash_lookup, this]() {
time_limit_->AdvanceDeterministicTime(static_cast<double>(num_hash_lookup) *
5e-8);
});
// TODO(user): We shouldn't consider ends for fixed intervals here. But
// then we should do a better job of computing the min-end of a subset of
// intervals from this disjunctive (like using fixed intervals even if there
// is no "before that variable" relationship). Ex: If a variable is after two
// intervals that cannot be both before a fixed one, we could propagate more.
index_to_end_vars_.clear();
int new_size = 0;
for (const auto task_time : window) {
const int task = task_time.task_index;
const AffineExpression& end_exp = helper_->Ends()[task];
// TODO(user): Handle generic affine relation?
if (end_exp.var == kNoIntegerVariable || end_exp.coeff != 1) continue;
window[new_size++] = task_time;
index_to_end_vars_.push_back(end_exp.var);
}
window = window.subspan(0, new_size);
// Because we use the cached value in the window, we don't really care
// on which order we process them.
precedence_relations_->CollectPrecedences(index_to_end_vars_, &before_);
const int size = before_.size();
for (int global_i = 0; global_i < size;) {
const int global_start_i = global_i;
const IntegerVariable var = before_[global_i].var;
DCHECK_NE(var, kNoIntegerVariable);
// Decode the set of task before var.
// Note that like in Propagate() we split this set of task into critical
// subpart as there is no point considering them together.
//
// TODO(user): If more than one set of task push the same variable, we
// probably only want to keep the best push? Maybe we want to process them
// in reverse order of what we do here?
indices_before_.clear();
IntegerValue local_start;
IntegerValue local_end;
for (; global_i < size; ++global_i) {
const EnforcedLinear2Bounds::PrecedenceData& data = before_[global_i];
if (data.var != var) break;
const int index = data.var_index;
const auto [t, start_of_t] = window[index];
if (global_i == global_start_i) { // First loop.
local_start = start_of_t;
local_end = local_start + helper_->SizeMin(t);
} else {
if (start_of_t >= local_end) break;
local_end += helper_->SizeMin(t);
}
indices_before_.push_back({index, data.lin2_index});
}
// No need to consider if we don't have at least two tasks before var.
const int num_before = indices_before_.size();
if (num_before < 2) continue;
skip_.assign(num_before, false);
// Heuristic.
// We will use the current end-min of all the task in indices_before_
// to skip task with an offset not large enough.
IntegerValue end_min_when_all_present = local_end;
// We will consider the end-min of all the subsets [i, num_items) to try to
// push var using the min-offset between var and items of such subset. This
// can be done in linear time by scanning from i = num_items - 1 to 0.
//
// Note that this needs the items in indices_before_ to be sorted by
// their shifted start min (it should be the case).
int best_index = -1;
const IntegerValue current_var_lb = integer_trail_.LowerBound(var);
IntegerValue best_new_lb = current_var_lb;
IntegerValue min_offset_at_best = kMinIntegerValue;
IntegerValue min_offset = kMaxIntegerValue;
IntegerValue sum_of_duration = 0;
for (int i = num_before; --i >= 0;) {
const auto [task_index, lin2_index] = indices_before_[i];
const TaskTime task_time = window[task_index];
const AffineExpression& end_exp = helper_->Ends()[task_time.task_index];
// TODO(user): The lookup here is a bit slow, so we avoid fetching
// the offset as much as possible.
++num_hash_lookup;
const IntegerValue inner_offset =
-linear2_bounds_->NonTrivialUpperBound(lin2_index);
DCHECK_NE(inner_offset, kMinIntegerValue);
// We have var >= end_exp.var + inner_offset, so
// var >= (end_exp.var + end_exp.constant)
// + (inner_offset - end_exp.constant)
// var >= task end + offset.
const IntegerValue offset = inner_offset - end_exp.constant;
// Heuristic: do not consider this relations if its offset is clearly bad.
const IntegerValue task_size = helper_->SizeMin(task_time.task_index);
if (end_min_when_all_present + offset <= best_new_lb) {
// This is true if we skipped all task so far in this block.
if (min_offset == kMaxIntegerValue) {
// If only one task is left, we can abort.
// This avoid a linear2_bounds_ lookup.
if (i == 1) break;
// Lower the end_min_when_all_present for better filtering later.
end_min_when_all_present -= task_size;
}
skip_[i] = true;
continue;
}
// Add this task to the current subset and compute the new bound.
min_offset = std::min(min_offset, offset);
sum_of_duration += task_size;
const IntegerValue start = task_time.time;
const IntegerValue new_lb = start + sum_of_duration + min_offset;
if (new_lb > best_new_lb) {
min_offset_at_best = min_offset;
best_new_lb = new_lb;
best_index = i;
}
}
// Push?
if (best_new_lb > current_var_lb) {
DCHECK_NE(best_index, -1);
helper_->ResetReason();
const IntegerValue window_start =
window[indices_before_[best_index].first].time;
for (int i = best_index; i < num_before; ++i) {
if (skip_[i]) continue;
const int ct = window[indices_before_[i].first].task_index;
helper_->AddPresenceReason(ct);
helper_->AddEnergyAfterReason(ct, helper_->SizeMin(ct), window_start);
// Fetch the explanation of (var - end) >= min_offset
// This is okay if a bit slow since we only do that when we push.
const auto [expr, ub] = EncodeDifferenceLowerThan(
helper_->Ends()[ct], var, -min_offset_at_best);
helper_->AddReasonForUpperBoundLowerThan(expr, ub);
}
++stats_.num_propagations;
if (!helper_->PushIntegerLiteral(
IntegerLiteral::GreaterOrEqual(var, best_new_lb))) {
return false;
}
}
}
return true;
}
int DisjunctivePrecedences::RegisterWith(GenericLiteralWatcher* watcher) {
// This propagator reach the fixed point in one go.
// Maybe not in corner cases, but since it is expansive, it is okay not to
// run it again right away
//
// Note also that technically, we don't need to be waked up if only the upper
// bound of the task changes, but this require to use more memory and the gain
// is unclear as this runs with the highest priority.
const int id = watcher->Register(this);
helper_->SetTimeDirection(time_direction_);
helper_->WatchAllTasks(id);
return id;
}
bool DisjunctiveNotLast::Propagate() {
if (!helper_->IsEnforced()) return true;
stats_.OnPropagate();
if (!helper_->SynchronizeAndSetTimeDirection(time_direction_)) {
++stats_.num_conflicts;
return false;
}
const auto task_by_negated_start_max =
helper_->TaskByIncreasingNegatedStartMax();
const auto task_by_increasing_shifted_start_min =
helper_->TaskByIncreasingShiftedStartMin();
TaskSet task_set(helper_->GetScratchTaskSet());
FixedCapacityVector<TaskTime>& start_min_window =
helper_->GetScratchTaskTimeVector1();
FixedCapacityVector<TaskTime>& start_max_window =
helper_->GetScratchTaskTimeVector2();
// Split problem into independent part.
//
// The situation is trickier here, and we use two windows:
// - The classical "start_min_window_" as in the other propagator.
// - A second window, that includes all the task with a start_max inside
// [window_start, window_end].
//
// Now, a task from the second window can be detected to be "not last" by only
// looking at the task in the first window. Tasks to the left do not cause
// issue for the task to be last, and tasks to the right will not lower the
// end-min of the task under consideration.
int queue_index = task_by_negated_start_max.size() - 1;
const int num_tasks = task_by_increasing_shifted_start_min.size();
for (int i = 0; i < num_tasks;) {
start_min_window.clear();
IntegerValue window_end = kMinIntegerValue;
for (; i < num_tasks; ++i) {
const auto [task, presence_lit, start_min] =
task_by_increasing_shifted_start_min[i];
if (!helper_->IsPresent(presence_lit)) continue;
if (start_min_window.empty()) {
start_min_window.push_back({task, start_min});
window_end = start_min + helper_->SizeMin(task);
} else if (start_min < window_end) {
start_min_window.push_back({task, start_min});
window_end += helper_->SizeMin(task);
} else {
break;
}
}
// Add to start_max_window_ all the task whose start_max
// fall into [window_start, window_end).
start_max_window.clear();
for (; queue_index >= 0; queue_index--) {
const auto [t, negated_start_max] =
task_by_negated_start_max[queue_index];
const IntegerValue start_max = -negated_start_max;
// Note that we add task whose presence is still unknown here.
if (start_max >= window_end) break;
if (helper_->IsAbsent(t)) continue;
start_max_window.push_back({t, start_max});
}
// If this is the case, we cannot propagate more than the detectable
// precedence propagator. Note that this continue must happen after we
// computed start_max_window_ though.
if (start_min_window.size() <= 1) continue;
// Process current window.
if (!start_max_window.empty() &&
!PropagateSubwindow(task_set, absl::MakeSpan(start_min_window),
absl::MakeSpan(start_max_window))) {
++stats_.num_conflicts;
return false;
}
}
stats_.EndWithoutConflicts();
return true;
}
bool DisjunctiveNotLast::PropagateSubwindow(
TaskSet& task_set, absl::Span<TaskTime> task_by_increasing_start_max,
absl::Span<TaskTime> task_by_increasing_end_max) {
for (TaskTime& entry : task_by_increasing_end_max) {
entry.time = helper_->EndMax(entry.task_index);
}
IncrementalSort(task_by_increasing_end_max.begin(),
task_by_increasing_end_max.end());
const IntegerValue threshold = task_by_increasing_end_max.back().time;
int queue_size = 0;
for (const TaskTime entry : task_by_increasing_start_max) {
const int task = entry.task_index;
const IntegerValue start_max = helper_->StartMax(task);
DCHECK(helper_->IsPresent(task));
if (start_max < threshold) {
task_by_increasing_start_max[queue_size++] = {task, start_max};
}
}
// If the size is one, we cannot propagate more than the detectable precedence
// propagator.
if (queue_size <= 1) return true;
task_by_increasing_start_max =
task_by_increasing_start_max.subspan(0, queue_size);
std::sort(task_by_increasing_start_max.begin(),
task_by_increasing_start_max.end());
task_set.Clear();
int queue_index = 0;
for (const auto task_time : task_by_increasing_end_max) {
const int t = task_time.task_index;
const IntegerValue end_max = task_time.time;
// We filtered absent task before, but it is possible that as we push
// bounds of optional tasks, more task become absent.
if (helper_->IsAbsent(t)) continue;
// task_set_ contains all the tasks that must start before the end-max of t.
// These are the only candidates that have a chance to decrease the end-max
// of t.
while (queue_index < queue_size) {
const auto to_insert = task_by_increasing_start_max[queue_index];
const IntegerValue start_max = to_insert.time;
if (end_max <= start_max) break;
const int task_index = to_insert.task_index;
DCHECK(helper_->IsPresent(task_index));
task_set.AddEntry({task_index, helper_->ShiftedStartMin(task_index),
helper_->SizeMin(task_index)});
++queue_index;
}
// In the following case, task t cannot be after all the critical tasks
// (i.e. it cannot be last):
//
// [(critical tasks)
// | <- t start-max
//
// So we can deduce that the end-max of t is smaller than or equal to the
// largest start-max of the critical tasks.
//
// Note that this works as well when the presence of t is still unknown.
int critical_index = 0;
const IntegerValue end_min_of_critical_tasks =
task_set.ComputeEndMin(/*task_to_ignore=*/t, &critical_index);
if (end_min_of_critical_tasks <= helper_->StartMax(t)) continue;
// Find the largest start-max of the critical tasks (excluding t). The
// end-max for t need to be smaller than or equal to this.
IntegerValue largest_ct_start_max = kMinIntegerValue;
const absl::Span<const TaskSet::Entry> sorted_tasks =
task_set.SortedTasks();
const int sorted_tasks_size = sorted_tasks.size();
for (int i = critical_index; i < sorted_tasks_size; ++i) {
const int ct = sorted_tasks[i].task;
if (t == ct) continue;
const IntegerValue start_max = helper_->StartMax(ct);
// If we already known that t is after ct we can have a tighter start-max.
if (start_max > largest_ct_start_max &&
helper_->GetCurrentMinDistanceBetweenTasks(ct, t) < 0) {
largest_ct_start_max = start_max;
}
}
// If we have any critical task, the test will always be true because
// of the tasks we put in task_set_.
DCHECK(largest_ct_start_max == kMinIntegerValue ||
end_max > largest_ct_start_max);
if (end_max > largest_ct_start_max) {
helper_->ResetReason();
const IntegerValue window_start = sorted_tasks[critical_index].start_min;
for (int i = critical_index; i < sorted_tasks_size; ++i) {
const int ct = sorted_tasks[i].task;
if (ct == t) continue;
helper_->AddPresenceReason(ct);
helper_->AddEnergyAfterReason(ct, sorted_tasks[i].size_min,
window_start);
if (helper_->GetCurrentMinDistanceBetweenTasks(ct, t) >= 0) {
helper_->AddReasonForBeingBeforeAssumingNoOverlap(ct, t);
} else {
helper_->AddStartMaxReason(ct, largest_ct_start_max);
}
}
// Add the reason for t, we only need the start-max.
helper_->AddStartMaxReason(t, end_min_of_critical_tasks - 1);
// If largest_ct_start_max == kMinIntegerValue, we have a conflict. To
// avoid integer overflow, we report it directly. This might happen
// because the task is known to be after all the other, and thus it cannot
// be "not last".
if (largest_ct_start_max == kMinIntegerValue) {
return helper_->ReportConflict();
}
// Enqueue the new end-max for t.
// Note that changing it will not influence the rest of the loop.
++stats_.num_propagations;
if (!helper_->DecreaseEndMax(t, largest_ct_start_max)) return false;
}
}
return true;
}
int DisjunctiveNotLast::RegisterWith(GenericLiteralWatcher* watcher) {
const int id = watcher->Register(this);
helper_->WatchAllTasks(id);
watcher->NotifyThatPropagatorMayNotReachFixedPointInOnePass(id);
return id;
}
bool DisjunctiveEdgeFinding::Propagate() {
if (!helper_->IsEnforced()) return true;
stats_.OnPropagate();
const int num_tasks = helper_->NumTasks();
if (!helper_->SynchronizeAndSetTimeDirection(time_direction_)) {
++stats_.num_conflicts;
return false;
}
is_gray_.resize(num_tasks, false);
non_gray_task_to_event_.resize(num_tasks);
FixedCapacityVector<TaskTime>& window = helper_->GetScratchTaskTimeVector1();
// This only contains non-gray tasks.
FixedCapacityVector<TaskTime>& task_by_increasing_end_max =
helper_->GetScratchTaskTimeVector2();
IntegerValue window_end = kMinIntegerValue;
for (const auto [task, presence_lit, shifted_smin] :
helper_->TaskByIncreasingShiftedStartMin()) {
if (helper_->IsAbsent(presence_lit)) continue;
// Note that we use the real start min here not the shifted one. This is
// because we might be able to push it if it is smaller than window end.
if (helper_->StartMin(task) < window_end) {
window.push_back({task, shifted_smin});
window_end += helper_->SizeMin(task);
continue;
}
// We need at least 3 tasks for the edge-finding to be different from
// detectable precedences.
if (window.size() > 2 &&
!PropagateSubwindow(window_end, absl::MakeSpan(window),
task_by_increasing_end_max)) {
++stats_.num_conflicts;
return false;
}
// Corner case: The propagation of the previous window might have made the
// current task absent even if it wasn't at the loop beginning.
if (helper_->IsAbsent(presence_lit)) {
window.clear();
window_end = kMinIntegerValue;
continue;
}
// Start of the next window.
window.clear();
window.push_back({task, shifted_smin});
window_end = shifted_smin + helper_->SizeMin(task);
}
if (window.size() > 2 &&
!PropagateSubwindow(window_end, absl::MakeSpan(window),
task_by_increasing_end_max)) {
++stats_.num_conflicts;
return false;
}
stats_.EndWithoutConflicts();
return true;
}
bool DisjunctiveEdgeFinding::PropagateSubwindow(
IntegerValue window_end_min, absl::Span<const TaskTime> window,
FixedCapacityVector<TaskTime>& task_by_increasing_end_max) {
// Cache the task end-max and abort early if possible.
task_by_increasing_end_max.clear();
for (const auto task_time : window) {
const int task = task_time.task_index;
DCHECK(!helper_->IsAbsent(task));
// We already mark all the non-present task as gray.
//
// Same for task with an end-max that is too large: Tasks that are not
// present can never trigger propagation or an overload checking failure.
// theta_tree_.GetOptionalEnvelope() is always <= window_end, so tasks whose
// end_max is >= window_end can never trigger propagation or failure either.
// Thus, those tasks can be marked as gray, which removes their contribution
// to theta right away.
const IntegerValue end_max = helper_->EndMax(task);
if (helper_->IsPresent(task) && end_max < window_end_min) {
is_gray_[task] = false;
task_by_increasing_end_max.push_back({task, end_max});
} else {
is_gray_[task] = true;
}
}
// If we have just 1 non-gray task, then this propagator does not propagate
// more than the detectable precedences, so we abort early.
if (task_by_increasing_end_max.size() < 2) return true;
std::sort(task_by_increasing_end_max.begin(),
task_by_increasing_end_max.end());
// Set up theta tree.
//
// Some task in the theta tree will be considered "gray".
// When computing the end-min of the sorted task, we will compute it for:
// - All the non-gray task
// - All the non-gray task + at most one gray task.
//
// TODO(user): it should be faster to initialize it all at once rather
// than calling AddOrUpdate() n times.
const int window_size = window.size();
event_size_.clear();
theta_tree_.Reset(window_size);
for (int event = 0; event < window_size; ++event) {
const TaskTime task_time = window[event];
const int task = task_time.task_index;
const IntegerValue energy_min = helper_->SizeMin(task);
event_size_.push_back(energy_min);
if (is_gray_[task]) {
theta_tree_.AddOrUpdateOptionalEvent(event, task_time.time, energy_min);
} else {
non_gray_task_to_event_[task] = event;
theta_tree_.AddOrUpdateEvent(event, task_time.time, energy_min,
energy_min);
}
}
// At each iteration we either transform a non-gray task into a gray one or
// remove a gray task, so this loop is linear in complexity.
while (true) {
DCHECK(!is_gray_[task_by_increasing_end_max.back().task_index]);
const IntegerValue non_gray_end_max =
task_by_increasing_end_max.back().time;
// Overload checking.
const IntegerValue non_gray_end_min = theta_tree_.GetEnvelope();
if (non_gray_end_min > non_gray_end_max) {
helper_->ResetReason();
// We need the reasons for the critical tasks to fall in:
const int critical_event =
theta_tree_.GetMaxEventWithEnvelopeGreaterThan(non_gray_end_max);
const IntegerValue window_start = window[critical_event].time;
const IntegerValue window_end =
theta_tree_.GetEnvelopeOf(critical_event) - 1;
for (int event = critical_event; event < window_size; event++) {
const int task = window[event].task_index;
if (is_gray_[task]) continue;
helper_->AddPresenceReason(task);
helper_->AddEnergyAfterReason(task, event_size_[event], window_start);
helper_->AddEndMaxReason(task, window_end);
}
return helper_->ReportConflict();
}
// Edge-finding.
// If we have a situation like:
// [(critical_task_with_gray_task)
// ]
// ^ end-max without the gray task.
//
// Then the gray task must be after all the critical tasks (all the non-gray
// tasks in the tree actually), otherwise there will be no way to schedule
// the critical_tasks inside their time window.
while (theta_tree_.GetOptionalEnvelope() > non_gray_end_max) {
const IntegerValue end_min_with_gray = theta_tree_.GetOptionalEnvelope();
int critical_event_with_gray;
int gray_event;
IntegerValue available_energy;
theta_tree_.GetEventsWithOptionalEnvelopeGreaterThan(
non_gray_end_max, &critical_event_with_gray, &gray_event,
&available_energy);
const int gray_task = window[gray_event].task_index;
DCHECK(is_gray_[gray_task]);
// This might happen in the corner case where more than one interval are
// controlled by the same Boolean.
if (helper_->IsAbsent(gray_task)) {
theta_tree_.RemoveEvent(gray_event);
continue;
}
// Since the gray task is after all the other, we have a new lower bound.
if (helper_->StartMin(gray_task) < non_gray_end_min) {
// The API is not ideal here. We just want the start of the critical
// tasks that explain the non_gray_end_min computed above.
const int critical_event =
theta_tree_.GetMaxEventWithEnvelopeGreaterThan(non_gray_end_min -
1);
// Even if we need less task to explain the overload, because we are
// going to explain the full non_gray_end_min, we can relax the
// explanation.
if (critical_event_with_gray > critical_event) {
critical_event_with_gray = critical_event;
}
const int first_event = critical_event_with_gray;
const int second_event = critical_event;
const IntegerValue first_start = window[first_event].time;
const IntegerValue second_start = window[second_event].time;
// window_end is chosen to be has big as possible and still have an
// overload if the gray task is not last.
//
// If gray_task is with variable duration, it is possible that it must
// be last just because is end-min is large.
bool use_energy_reason = true;
IntegerValue window_end;
if (helper_->EndMin(gray_task) > non_gray_end_max) {
// This is actually a form of detectable precedence.
//
// TODO(user): We could relax the reason more, but this happen really
// rarely it seems.
use_energy_reason = false;
window_end = helper_->EndMin(gray_task) - 1;
} else {
window_end = end_min_with_gray - 1;
}
CHECK_GE(window_end, non_gray_end_max);
// The non-gray part of the explanation as detailed above.
helper_->ResetReason();
bool all_before = true;
for (int event = first_event; event < window_size; event++) {
const int task = window[event].task_index;
if (is_gray_[task]) continue;
helper_->AddPresenceReason(task);
helper_->AddEnergyAfterReason(
task, event_size_[event],
event >= second_event ? second_start : first_start);
const IntegerValue dist =
helper_->GetCurrentMinDistanceBetweenTasks(task, gray_task);
if (dist >= 0) {
helper_->AddReasonForBeingBeforeAssumingNoOverlap(task, gray_task);
} else {
all_before = false;
helper_->AddEndMaxReason(task, window_end);
}
}
// Add the reason for the gray_task (we don't need the end-max or
// presence reason) needed for the precedences.
if (!all_before) {
if (use_energy_reason) {
helper_->AddEnergyAfterReason(gray_task, event_size_[gray_event],
first_start);
} else {
helper_->AddEndMinReason(gray_task, helper_->EndMin(gray_task));
}
}
// Process detected precedence.
if (helper_->CurrentDecisionLevel() == 0 &&
helper_->IsPresent(gray_task)) {
for (int i = first_event; i < window_size; ++i) {
const int task = window[i].task_index;
if (!is_gray_[task]) {
if (!helper_->NotifyLevelZeroPrecedence(task, gray_task)) {
return false;
}
}
}
}
// Enqueue the new start-min for gray_task.
//
// TODO(user): propagate the precedence Boolean here too? I think it
// will be more powerful. Even if eventually all these precedence will
// become detectable (see Petr Villim PhD).
++stats_.num_propagations;
if (!helper_->IncreaseStartMin(gray_task, non_gray_end_min)) {
return false;
}
}
// Remove the gray_task.
theta_tree_.RemoveEvent(gray_event);
}
// Stop before we get just one non-gray task.
if (task_by_increasing_end_max.size() <= 2) break;
// Stop if the min of end_max is too big.
if (task_by_increasing_end_max[0].time >=
theta_tree_.GetOptionalEnvelope()) {
break;
}
// Make the non-gray task with larger end-max gray.
const int new_gray_task = task_by_increasing_end_max.back().task_index;
task_by_increasing_end_max.pop_back();
const int new_gray_event = non_gray_task_to_event_[new_gray_task];
DCHECK(!is_gray_[new_gray_task]);
is_gray_[new_gray_task] = true;
theta_tree_.AddOrUpdateOptionalEvent(new_gray_event,
window[new_gray_event].time,
event_size_[new_gray_event]);
}
return true;
}
int DisjunctiveEdgeFinding::RegisterWith(GenericLiteralWatcher* watcher) {
const int id = watcher->Register(this);
helper_->SetTimeDirection(time_direction_);
helper_->WatchAllTasks(id);
watcher->NotifyThatPropagatorMayNotReachFixedPointInOnePass(id);
return id;
}
} // namespace sat
} // namespace operations_research
Reference in New Issue View Git Blame Copy Permalink