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ortools-clone/ortools/sat/precedences.cc
Corentin Le Molgat c34026b101 Bump copyright to 2025 
note: done using
```sh
git grep -l "2010-2024 Google" | xargs sed -i 's/2010-2024 Google/2010-2025 Google/'
```
2025-01-10 11:33:35 +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 "ortools/sat/precedences.h"
#include <stdint.h>
#include <algorithm>
#include <deque>
#include <memory>
#include <string>
#include <utility>
#include <vector>
#include "absl/cleanup/cleanup.h"
#include "absl/container/btree_set.h"
#include "absl/container/flat_hash_map.h"
#include "absl/container/flat_hash_set.h"
#include "absl/container/inlined_vector.h"
#include "absl/log/check.h"
#include "absl/meta/type_traits.h"
#include "absl/types/span.h"
#include "ortools/base/logging.h"
#include "ortools/base/stl_util.h"
#include "ortools/base/strong_vector.h"
#include "ortools/graph/graph.h"
#include "ortools/graph/topologicalsorter.h"
#include "ortools/sat/clause.h"
#include "ortools/sat/cp_constraints.h"
#include "ortools/sat/integer.h"
#include "ortools/sat/integer_base.h"
#include "ortools/sat/model.h"
#include "ortools/sat/sat_base.h"
#include "ortools/sat/sat_solver.h"
#include "ortools/sat/synchronization.h"
#include "ortools/sat/util.h"
#include "ortools/util/bitset.h"
#include "ortools/util/logging.h"
#include "ortools/util/strong_integers.h"
#include "ortools/util/time_limit.h"
namespace operations_research {
namespace sat {
bool PrecedenceRelations::Add(IntegerVariable tail, IntegerVariable head,
IntegerValue offset) {
// Ignore trivial relation: tail + offset <= head.
if (integer_trail_->LevelZeroUpperBound(tail) + offset <=
integer_trail_->LevelZeroLowerBound(head)) {
return false;
}
// TODO(user): Return infeasible if tail == head and offset > 0.
// TODO(user): if tail = Negation(head) also update Domain.
if (tail == head) return false;
// Add to root_relations_.
//
// TODO(user): AddInternal() only returns true if this is the first relation
// between head and tail. But we can still avoid an extra lookup.
if (offset <= GetOffset(tail, head)) return false;
AddInternal(tail, head, offset);
// If we are not built, make sure there is enough room in the graph.
// TODO(user): Alternatively, force caller to do a Resize().
const int max_node =
std::max(PositiveVariable(tail), PositiveVariable(head)).value() + 1;
if (!is_built_ && max_node >= graph_.num_nodes()) {
graph_.AddNode(max_node);
}
return true;
}
void PrecedenceRelations::PushConditionalRelation(
absl::Span<const Literal> enforcements, IntegerVariable a,
IntegerVariable b, IntegerValue rhs) {
// This must be currently true.
if (DEBUG_MODE) {
for (const Literal l : enforcements) {
CHECK(trail_->Assignment().LiteralIsTrue(l));
}
}
if (enforcements.empty() || trail_->CurrentDecisionLevel() == 0) {
Add(a, NegationOf(b), -rhs);
return;
}
// Ignore if no better than best_relations, otherwise increase it.
const auto key = GetKey(a, b);
{
const auto [it, inserted] = best_relations_.insert({key, rhs});
if (!inserted) {
if (rhs >= it->second) return; // Ignore.
it->second = rhs;
}
}
const int new_index = conditional_stack_.size();
const auto [it, inserted] = conditional_relations_.insert({key, new_index});
if (inserted) {
CreateLevelEntryIfNeeded();
conditional_stack_.emplace_back(/*prev_entry=*/-1, rhs, key, enforcements);
const int new_size = std::max(a.value(), b.value()) + 1;
if (new_size > conditional_after_.size()) {
conditional_after_.resize(new_size);
}
conditional_after_[a].push_back(NegationOf(b));
conditional_after_[b].push_back(NegationOf(a));
} else {
// We should only decrease because we ignored entry worse than the one in
// best_relations_.
const int prev_entry = it->second;
DCHECK_LT(rhs, conditional_stack_[prev_entry].rhs);
// Update.
it->second = new_index;
CreateLevelEntryIfNeeded();
conditional_stack_.emplace_back(prev_entry, rhs, key, enforcements);
}
}
void PrecedenceRelations::CreateLevelEntryIfNeeded() {
const int current = trail_->CurrentDecisionLevel();
if (!level_to_stack_size_.empty() &&
level_to_stack_size_.back().first == current)
return;
level_to_stack_size_.push_back({current, conditional_stack_.size()});
}
// We only pop what is needed.
void PrecedenceRelations::SetLevel(int level) {
while (!level_to_stack_size_.empty() &&
level_to_stack_size_.back().first > level) {
const int target = level_to_stack_size_.back().second;
DCHECK_GE(conditional_stack_.size(), target);
while (conditional_stack_.size() > target) {
const ConditionalEntry& back = conditional_stack_.back();
if (back.prev_entry != -1) {
conditional_relations_[back.key] = back.prev_entry;
UpdateBestRelation(back.key, conditional_stack_[back.prev_entry].rhs);
} else {
UpdateBestRelation(back.key, kMaxIntegerValue);
conditional_relations_.erase(back.key);
DCHECK_EQ(conditional_after_[back.key.first].back(),
NegationOf(back.key.second));
DCHECK_EQ(conditional_after_[back.key.second].back(),
NegationOf(back.key.first));
conditional_after_[back.key.first].pop_back();
conditional_after_[back.key.second].pop_back();
}
conditional_stack_.pop_back();
}
level_to_stack_size_.pop_back();
}
}
IntegerValue PrecedenceRelations::GetOffset(IntegerVariable a,
IntegerVariable b) const {
const auto it = root_relations_.find(GetKey(a, NegationOf(b)));
if (it != root_relations_.end()) {
return -it->second;
}
return kMinIntegerValue;
}
absl::Span<const Literal> PrecedenceRelations::GetConditionalEnforcements(
IntegerVariable a, IntegerVariable b) const {
const auto it = conditional_relations_.find(GetKey(a, NegationOf(b)));
if (it == conditional_relations_.end()) return {};
const ConditionalEntry& entry = conditional_stack_[it->second];
if (DEBUG_MODE) {
for (const Literal l : entry.enforcements) {
CHECK(trail_->Assignment().LiteralIsTrue(l));
}
}
const IntegerValue root_level_offset = GetOffset(a, b);
const IntegerValue conditional_offset = -entry.rhs;
if (conditional_offset <= root_level_offset) return {};
DCHECK_EQ(entry.rhs, -GetConditionalOffset(a, b));
return entry.enforcements;
}
IntegerValue PrecedenceRelations::GetConditionalOffset(
IntegerVariable a, IntegerVariable b) const {
const auto it = best_relations_.find(GetKey(a, NegationOf(b)));
if (it != best_relations_.end()) {
return -it->second;
}
DCHECK(!root_relations_.contains(GetKey(a, NegationOf(b))));
DCHECK(!conditional_relations_.contains(GetKey(a, NegationOf(b))));
return kMinIntegerValue;
}
void PrecedenceRelations::Build() {
if (is_built_) return;
is_built_ = true;
const int num_nodes = graph_.num_nodes();
util_intops::StrongVector<IntegerVariable, std::vector<IntegerVariable>>
before(num_nodes);
// We will construct a graph with the current relation from all_relations_.
// And use this to compute the "closure".
CHECK(arc_offsets_.empty());
graph_.ReserveArcs(2 * root_relations_.size());
std::vector<
std::pair<std::pair<IntegerVariable, IntegerVariable>, IntegerValue>>
root_relations_sorted(root_relations_.begin(), root_relations_.end());
std::sort(root_relations_sorted.begin(), root_relations_sorted.end());
for (const auto [var_pair, negated_offset] : root_relations_sorted) {
// TODO(user): Support negative offset?
//
// Note that if we only have >= 0 ones, if we do have a cycle, we could
// make sure all variales are the same, and otherwise, we have a DAG or a
// conflict.
const IntegerValue offset = -negated_offset;
if (offset < 0) continue;
// We have two arcs.
{
const IntegerVariable tail = var_pair.first;
const IntegerVariable head = NegationOf(var_pair.second);
graph_.AddArc(tail.value(), head.value());
arc_offsets_.push_back(offset);
CHECK_LT(var_pair.second, before.size());
before[head].push_back(tail);
}
{
const IntegerVariable tail = var_pair.second;
const IntegerVariable head = NegationOf(var_pair.first);
graph_.AddArc(tail.value(), head.value());
arc_offsets_.push_back(offset);
CHECK_LT(var_pair.second, before.size());
before[head].push_back(tail);
}
}
std::vector<int> permutation;
graph_.Build(&permutation);
util::Permute(permutation, &arc_offsets_);
// Is it a DAG?
// Get a topological order of the DAG formed by all the arcs that are present.
//
// TODO(user): This can fail if we don't have a DAG. We could just skip Bad
// edges instead, and have a sub-DAG as an heuristic. Or analyze the arc
// weight and make sure cycle are not an issue. We can also start with arcs
// with strictly positive weight.
//
// TODO(user): Only explore the sub-graph reachable from "vars".
DenseIntStableTopologicalSorter sorter(num_nodes);
for (int arc = 0; arc < graph_.num_arcs(); ++arc) {
sorter.AddEdge(graph_.Tail(arc), graph_.Head(arc));
}
int next;
bool graph_has_cycle = false;
topological_order_.clear();
while (sorter.GetNext(&next, &graph_has_cycle, nullptr)) {
topological_order_.push_back(IntegerVariable(next));
if (graph_has_cycle) {
is_dag_ = false;
return;
}
}
is_dag_ = !graph_has_cycle;
// Lets build full precedences if we don't have too many of them.
// TODO(user): Also do that if we don't have a DAG?
if (!is_dag_) return;
int work = 0;
const int kWorkLimit = 1e6;
for (const IntegerVariable tail_var : topological_order_) {
if (++work > kWorkLimit) break;
for (const int arc : graph_.OutgoingArcs(tail_var.value())) {
DCHECK_EQ(tail_var.value(), graph_.Tail(arc));
const IntegerVariable head_var = IntegerVariable(graph_.Head(arc));
const IntegerValue arc_offset = arc_offsets_[arc];
if (++work > kWorkLimit) break;
if (AddInternal(tail_var, head_var, arc_offset)) {
before[head_var].push_back(tail_var);
}
for (const IntegerVariable before_var : before[tail_var]) {
if (++work > kWorkLimit) break;
const IntegerValue offset =
-root_relations_.at(GetKey(before_var, NegationOf(tail_var))) +
arc_offset;
if (AddInternal(before_var, head_var, offset)) {
before[head_var].push_back(before_var);
}
}
}
}
VLOG(2) << "Full precedences. Work=" << work
<< " Relations=" << root_relations_.size();
}
void PrecedenceRelations::ComputeFullPrecedences(
absl::Span<const IntegerVariable> vars,
std::vector<FullIntegerPrecedence>* output) {
output->clear();
if (!is_built_) Build();
if (!is_dag_) return;
VLOG(2) << "num_nodes: " << graph_.num_nodes()
<< " num_arcs: " << graph_.num_arcs() << " is_dag: " << is_dag_;
// Compute all precedences.
// We loop over the node in topological order, and we maintain for all
// variable we encounter, the list of "to_consider" variables that are before.
//
// TODO(user): use vector of fixed size.
absl::flat_hash_set<IntegerVariable> is_interesting;
absl::flat_hash_set<IntegerVariable> to_consider(vars.begin(), vars.end());
absl::flat_hash_map<IntegerVariable,
absl::flat_hash_map<IntegerVariable, IntegerValue>>
vars_before_with_offset;
absl::flat_hash_map<IntegerVariable, IntegerValue> tail_map;
for (const IntegerVariable tail_var : topological_order_) {
if (!to_consider.contains(tail_var) &&
!vars_before_with_offset.contains(tail_var)) {
continue;
}
// We copy the data for tail_var here, because the pointer is not stable.
// TODO(user): optimize when needed.
tail_map.clear();
{
const auto it = vars_before_with_offset.find(tail_var);
if (it != vars_before_with_offset.end()) {
tail_map = it->second;
}
}
for (const int arc : graph_.OutgoingArcs(tail_var.value())) {
CHECK_EQ(tail_var.value(), graph_.Tail(arc));
const IntegerVariable head_var = IntegerVariable(graph_.Head(arc));
const IntegerValue arc_offset = arc_offsets_[arc];
// No need to create an empty entry in this case.
if (tail_map.empty() && !to_consider.contains(tail_var)) continue;
auto& to_update = vars_before_with_offset[head_var];
for (const auto& [var_before, offset] : tail_map) {
if (!to_update.contains(var_before)) {
to_update[var_before] = arc_offset + offset;
} else {
to_update[var_before] =
std::max(arc_offset + offset, to_update[var_before]);
}
}
if (to_consider.contains(tail_var)) {
if (!to_update.contains(tail_var)) {
to_update[tail_var] = arc_offset;
} else {
to_update[tail_var] = std::max(arc_offset, to_update[tail_var]);
}
}
// Small filtering heuristic: if we have (before) < tail, and tail < head,
// we really do not need to list (before, tail) < head. We only need that
// if the list of variable before head contains some variable that are not
// already before tail.
if (to_update.size() > tail_map.size() + 1) {
is_interesting.insert(head_var);
} else {
is_interesting.erase(head_var);
}
}
// Extract the output for tail_var. Because of the topological ordering, the
// data for tail_var is already final now.
//
// TODO(user): Release the memory right away.
if (!is_interesting.contains(tail_var)) continue;
if (tail_map.size() == 1) continue;
FullIntegerPrecedence data;
data.var = tail_var;
IntegerValue min_offset = kMaxIntegerValue;
for (int i = 0; i < vars.size(); ++i) {
const auto offset_it = tail_map.find(vars[i]);
if (offset_it == tail_map.end()) continue;
data.indices.push_back(i);
data.offsets.push_back(offset_it->second);
min_offset = std::min(data.offsets.back(), min_offset);
}
output->push_back(std::move(data));
}
}
void PrecedenceRelations::CollectPrecedences(
absl::Span<const IntegerVariable> vars,
std::vector<PrecedenceData>* output) {
// +1 for the negation.
const int needed_size =
std::max(after_.size(), conditional_after_.size()) + 1;
var_to_degree_.resize(needed_size);
var_to_last_index_.resize(needed_size);
var_with_positive_degree_.resize(needed_size);
tmp_precedences_.clear();
// We first compute the degree/size in order to perform the transposition.
// Note that we also remove duplicates.
int num_relevants = 0;
IntegerVariable* var_with_positive_degree = var_with_positive_degree_.data();
int* var_to_degree = var_to_degree_.data();
int* var_to_last_index = var_to_last_index_.data();
const auto process = [&](int index, absl::Span<const IntegerVariable> v) {
for (const IntegerVariable after : v) {
DCHECK_LT(after, needed_size);
if (var_to_degree[after.value()] == 0) {
var_with_positive_degree[num_relevants++] = after;
} else {
// We do not want duplicates.
if (var_to_last_index[after.value()] == index) continue;
}
tmp_precedences_.push_back({after, index});
var_to_degree[after.value()]++;
var_to_last_index[after.value()] = index;
}
};
for (int index = 0; index < vars.size(); ++index) {
const IntegerVariable var = vars[index];
if (var < after_.size()) {
process(index, after_[var]);
}
if (var < conditional_after_.size()) {
process(index, conditional_after_[var]);
}
}
// Permute tmp_precedences_ into the output to put it in the correct order.
// For that we transform var_to_degree to point to the first position of
// each lbvar in the output vector.
int start = 0;
for (int i = 0; i < num_relevants; ++i) {
const IntegerVariable var = var_with_positive_degree[i];
const int degree = var_to_degree[var.value()];
if (degree > 1) {
var_to_degree[var.value()] = start;
start += degree;
} else {
// Optimization: we remove degree one relations.
var_to_degree[var.value()] = -1;
}
}
output->resize(start);
for (const auto& precedence : tmp_precedences_) {
// Note that it is okay to increase the -1 pos since they appear only once.
const int pos = var_to_degree[precedence.var.value()]++;
if (pos < 0) continue;
(*output)[pos] = precedence;
}
// Cleanup var_to_degree, note that we don't need to clean
// var_to_last_index_.
for (int i = 0; i < num_relevants; ++i) {
const IntegerVariable var = var_with_positive_degree[i];
var_to_degree[var.value()] = 0;
}
}
namespace {
void AppendLowerBoundReasonIfValid(IntegerVariable var,
const IntegerTrail& i_trail,
std::vector<IntegerLiteral>* reason) {
if (var != kNoIntegerVariable) {
reason->push_back(i_trail.LowerBoundAsLiteral(var));
}
}
} // namespace
PrecedencesPropagator::~PrecedencesPropagator() {
if (!VLOG_IS_ON(1)) return;
if (shared_stats_ == nullptr) return;
std::vector<std::pair<std::string, int64_t>> stats;
stats.push_back({"precedences/num_cycles", num_cycles_});
stats.push_back({"precedences/num_pushes", num_pushes_});
stats.push_back(
{"precedences/num_enforcement_pushes", num_enforcement_pushes_});
shared_stats_->AddStats(stats);
}
bool PrecedencesPropagator::Propagate(Trail* trail) { return Propagate(); }
bool PrecedencesPropagator::Propagate() {
while (propagation_trail_index_ < trail_->Index()) {
const Literal literal = (*trail_)[propagation_trail_index_++];
if (literal.Index() >= literal_to_new_impacted_arcs_.size()) continue;
// IMPORTANT: Because of the way Untrail() work, we need to add all the
// potential arcs before we can abort. It is why we iterate twice here.
for (const ArcIndex arc_index :
literal_to_new_impacted_arcs_[literal.Index()]) {
if (--arc_counts_[arc_index] == 0) {
const ArcInfo& arc = arcs_[arc_index];
PushConditionalRelations(arc);
impacted_arcs_[arc.tail_var].push_back(arc_index);
}
}
// Iterate again to check for a propagation and indirectly update
// modified_vars_.
for (const ArcIndex arc_index :
literal_to_new_impacted_arcs_[literal.Index()]) {
if (arc_counts_[arc_index] > 0) continue;
const ArcInfo& arc = arcs_[arc_index];
const IntegerValue new_head_lb =
integer_trail_->LowerBound(arc.tail_var) + ArcOffset(arc);
if (new_head_lb > integer_trail_->LowerBound(arc.head_var)) {
if (!EnqueueAndCheck(arc, new_head_lb, trail_)) return false;
}
}
}
// Do the actual propagation of the IntegerVariable bounds.
InitializeBFQueueWithModifiedNodes();
if (!BellmanFordTarjan(trail_)) return false;
// We can only test that no propagation is left if we didn't enqueue new
// literal in the presence of optional variables.
//
// TODO(user): Because of our code to deal with InPropagationLoop(), this is
// not always true. Find a cleaner way to DCHECK() while not failing in this
// corner case.
if (/*DISABLES CODE*/ (false) &&
propagation_trail_index_ == trail_->Index()) {
DCHECK(NoPropagationLeft(*trail_));
}
// Propagate the presence literals of the arcs that can't be added.
PropagateOptionalArcs(trail_);
// Clean-up modified_vars_ to do as little as possible on the next call.
modified_vars_.ClearAndResize(integer_trail_->NumIntegerVariables());
return true;
}
bool PrecedencesPropagator::PropagateOutgoingArcs(IntegerVariable var) {
CHECK_NE(var, kNoIntegerVariable);
if (var >= impacted_arcs_.size()) return true;
for (const ArcIndex arc_index : impacted_arcs_[var]) {
const ArcInfo& arc = arcs_[arc_index];
const IntegerValue new_head_lb =
integer_trail_->LowerBound(arc.tail_var) + ArcOffset(arc);
if (new_head_lb > integer_trail_->LowerBound(arc.head_var)) {
if (!EnqueueAndCheck(arc, new_head_lb, trail_)) return false;
}
}
return true;
}
// TODO(user): Remove literal fixed at level zero from there.
void PrecedencesPropagator::PushConditionalRelations(const ArcInfo& arc) {
// We currently do not handle variable size in the reasons.
// TODO(user): we could easily take a level zero ArcOffset() instead, or
// add this to the reason though.
if (arc.offset_var != kNoIntegerVariable) return;
const IntegerValue offset = ArcOffset(arc);
relations_->PushConditionalRelation(arc.presence_literals, arc.tail_var,
NegationOf(arc.head_var), -offset);
}
void PrecedencesPropagator::Untrail(const Trail& trail, int trail_index) {
if (propagation_trail_index_ > trail_index) {
// This means that we already propagated all there is to propagate
// at the level trail_index, so we can safely clear modified_vars_ in case
// it wasn't already done.
modified_vars_.ClearAndResize(integer_trail_->NumIntegerVariables());
}
while (propagation_trail_index_ > trail_index) {
const Literal literal = trail[--propagation_trail_index_];
if (literal.Index() >= literal_to_new_impacted_arcs_.size()) continue;
for (const ArcIndex arc_index :
literal_to_new_impacted_arcs_[literal.Index()]) {
if (arc_counts_[arc_index]++ == 0) {
const ArcInfo& arc = arcs_[arc_index];
impacted_arcs_[arc.tail_var].pop_back();
}
}
}
}
void PrecedencesPropagator::AdjustSizeFor(IntegerVariable i) {
const int index = std::max(i.value(), NegationOf(i).value());
if (index >= impacted_arcs_.size()) {
// TODO(user): only watch lower bound of the relevant variable instead
// of watching everything in [0, max_index_of_variable_used_in_this_class).
for (IntegerVariable var(impacted_arcs_.size()); var <= index; ++var) {
watcher_->WatchLowerBound(var, watcher_id_);
}
impacted_arcs_.resize(index + 1);
impacted_potential_arcs_.resize(index + 1);
}
}
void PrecedencesPropagator::AddArc(
IntegerVariable tail, IntegerVariable head, IntegerValue offset,
IntegerVariable offset_var, absl::Span<const Literal> presence_literals) {
AdjustSizeFor(tail);
AdjustSizeFor(head);
if (offset_var != kNoIntegerVariable) AdjustSizeFor(offset_var);
// This arc is present iff all the literals here are true.
absl::InlinedVector<Literal, 6> enforcement_literals;
{
for (const Literal l : presence_literals) {
enforcement_literals.push_back(l);
}
gtl::STLSortAndRemoveDuplicates(&enforcement_literals);
if (trail_->CurrentDecisionLevel() == 0) {
int new_size = 0;
for (const Literal l : enforcement_literals) {
if (trail_->Assignment().LiteralIsTrue(Literal(l))) {
continue; // At true, ignore this literal.
} else if (trail_->Assignment().LiteralIsFalse(Literal(l))) {
return; // At false, ignore completely this arc.
}
enforcement_literals[new_size++] = l;
}
enforcement_literals.resize(new_size);
}
}
if (head == tail) {
// A self-arc is either plain SAT or plain UNSAT or it forces something on
// the given offset_var or presence_literal_index. In any case it could be
// presolved in something more efficient.
VLOG(1) << "Self arc! This could be presolved. "
<< "var:" << tail << " offset:" << offset
<< " offset_var:" << offset_var
<< " conditioned_by:" << presence_literals;
}
// Remove the offset_var if it is fixed.
// TODO(user): We should also handle the case where tail or head is fixed.
if (offset_var != kNoIntegerVariable) {
const IntegerValue lb = integer_trail_->LevelZeroLowerBound(offset_var);
if (lb == integer_trail_->LevelZeroUpperBound(offset_var)) {
offset += lb;
offset_var = kNoIntegerVariable;
}
}
// Deal first with impacted_potential_arcs_/potential_arcs_.
if (!enforcement_literals.empty()) {
const OptionalArcIndex arc_index(potential_arcs_.size());
potential_arcs_.push_back(
{tail, head, offset, offset_var, enforcement_literals});
impacted_potential_arcs_[tail].push_back(arc_index);
impacted_potential_arcs_[NegationOf(head)].push_back(arc_index);
if (offset_var != kNoIntegerVariable) {
impacted_potential_arcs_[offset_var].push_back(arc_index);
}
}
// Now deal with impacted_arcs_/arcs_.
struct InternalArc {
IntegerVariable tail_var;
IntegerVariable head_var;
IntegerVariable offset_var;
};
std::vector<InternalArc> to_add;
if (offset_var == kNoIntegerVariable) {
// a + offset <= b and -b + offset <= -a
to_add.push_back({tail, head, kNoIntegerVariable});
to_add.push_back({NegationOf(head), NegationOf(tail), kNoIntegerVariable});
} else {
// tail (a) and offset_var (b) are symmetric, so we add:
// - a + b + offset <= c
to_add.push_back({tail, head, offset_var});
to_add.push_back({offset_var, head, tail});
// - a - c + offset <= -b
to_add.push_back({tail, NegationOf(offset_var), NegationOf(head)});
to_add.push_back({NegationOf(head), NegationOf(offset_var), tail});
// - b - c + offset <= -a
to_add.push_back({offset_var, NegationOf(tail), NegationOf(head)});
to_add.push_back({NegationOf(head), NegationOf(tail), offset_var});
}
for (const InternalArc a : to_add) {
// Since we add a new arc, we will need to consider its tail during the next
// propagation. Note that the size of modified_vars_ will be automatically
// updated when new integer variables are created since we register it with
// IntegerTrail in this class constructor.
//
// TODO(user): Adding arcs and then calling Untrail() before Propagate()
// will cause this mecanism to break. Find a more robust implementation.
//
// TODO(user): In some rare corner case, rescanning the whole list of arc
// leaving tail_var can make AddVar() have a quadratic complexity where it
// shouldn't. A better solution would be to see if this new arc currently
// propagate something, and if it does, just update the lower bound of
// a.head_var and let the normal "is modified" mecanism handle any eventual
// follow up propagations.
modified_vars_.Set(a.tail_var);
// If a.head_var is optional, we can potentially remove some literal from
// enforcement_literals.
const ArcIndex arc_index(arcs_.size());
arcs_.push_back(
{a.tail_var, a.head_var, offset, a.offset_var, enforcement_literals});
auto& presence_literals = arcs_.back().presence_literals;
if (presence_literals.empty()) {
impacted_arcs_[a.tail_var].push_back(arc_index);
} else {
for (const Literal l : presence_literals) {
if (l.Index() >= literal_to_new_impacted_arcs_.size()) {
literal_to_new_impacted_arcs_.resize(l.Index().value() + 1);
}
literal_to_new_impacted_arcs_[l.Index()].push_back(arc_index);
}
}
if (trail_->CurrentDecisionLevel() == 0) {
arc_counts_.push_back(presence_literals.size());
} else {
arc_counts_.push_back(0);
for (const Literal l : presence_literals) {
if (!trail_->Assignment().LiteralIsTrue(l)) {
++arc_counts_.back();
}
}
CHECK(presence_literals.empty() || arc_counts_.back() > 0);
}
}
}
bool PrecedencesPropagator::AddPrecedenceWithOffsetIfNew(IntegerVariable i1,
IntegerVariable i2,
IntegerValue offset) {
DCHECK_EQ(trail_->CurrentDecisionLevel(), 0);
if (i1 < impacted_arcs_.size() && i2 < impacted_arcs_.size()) {
for (const ArcIndex index : impacted_arcs_[i1]) {
const ArcInfo& arc = arcs_[index];
if (arc.head_var == i2) {
const IntegerValue current = ArcOffset(arc);
if (offset <= current) {
return false;
} else {
// TODO(user): Modify arc in place!
}
break;
}
}
}
AddPrecedenceWithOffset(i1, i2, offset);
return true;
}
// TODO(user): On jobshop problems with a lot of tasks per machine (500), this
// takes up a big chunk of the running time even before we find a solution.
// This is because, for each lower bound changed, we inspect 500 arcs even
// though they will never be propagated because the other bound is still at the
// horizon. Find an even sparser algorithm?
void PrecedencesPropagator::PropagateOptionalArcs(Trail* trail) {
for (const IntegerVariable var : modified_vars_.PositionsSetAtLeastOnce()) {
// The variables are not in increasing order, so we need to continue.
if (var >= impacted_potential_arcs_.size()) continue;
// Note that we can currently check the same ArcInfo up to 3 times, one for
// each of the arc variables: tail, NegationOf(head) and offset_var.
for (const OptionalArcIndex arc_index : impacted_potential_arcs_[var]) {
const ArcInfo& arc = potential_arcs_[arc_index];
int num_not_true = 0;
Literal to_propagate;
for (const Literal l : arc.presence_literals) {
if (!trail->Assignment().LiteralIsTrue(l)) {
++num_not_true;
to_propagate = l;
}
}
if (num_not_true != 1) continue;
if (trail->Assignment().LiteralIsFalse(to_propagate)) continue;
// Test if this arc can be present or not.
// Important arc.tail_var can be different from var here.
const IntegerValue tail_lb = integer_trail_->LowerBound(arc.tail_var);
const IntegerValue head_ub = integer_trail_->UpperBound(arc.head_var);
if (tail_lb + ArcOffset(arc) > head_ub) {
integer_reason_.clear();
integer_reason_.push_back(
integer_trail_->LowerBoundAsLiteral(arc.tail_var));
integer_reason_.push_back(
integer_trail_->UpperBoundAsLiteral(arc.head_var));
AppendLowerBoundReasonIfValid(arc.offset_var, *integer_trail_,
&integer_reason_);
literal_reason_.clear();
for (const Literal l : arc.presence_literals) {
if (l != to_propagate) literal_reason_.push_back(l.Negated());
}
++num_enforcement_pushes_;
integer_trail_->EnqueueLiteral(to_propagate.Negated(), literal_reason_,
integer_reason_);
}
}
}
}
IntegerValue PrecedencesPropagator::ArcOffset(const ArcInfo& arc) const {
return arc.offset + (arc.offset_var == kNoIntegerVariable
? IntegerValue(0)
: integer_trail_->LowerBound(arc.offset_var));
}
bool PrecedencesPropagator::EnqueueAndCheck(const ArcInfo& arc,
IntegerValue new_head_lb,
Trail* trail) {
++num_pushes_;
DCHECK_GT(new_head_lb, integer_trail_->LowerBound(arc.head_var));
// Compute the reason for new_head_lb.
//
// TODO(user): do like for clause and keep the negation of
// arc.presence_literals? I think we could change the integer.h API to accept
// true literal like for IntegerVariable, it is really confusing currently.
literal_reason_.clear();
for (const Literal l : arc.presence_literals) {
literal_reason_.push_back(l.Negated());
}
integer_reason_.clear();
integer_reason_.push_back(integer_trail_->LowerBoundAsLiteral(arc.tail_var));
AppendLowerBoundReasonIfValid(arc.offset_var, *integer_trail_,
&integer_reason_);
// The code works without this block since Enqueue() below can already take
// care of conflicts. However, it is better to deal with the conflict
// ourselves because we can be smarter about the reason this way.
//
// The reason for a "precedence" conflict is always a linear reason
// involving the tail lower_bound, the head upper bound and eventually the
// size lower bound. Because of that, we can use the RelaxLinearReason()
// code.
if (new_head_lb > integer_trail_->UpperBound(arc.head_var)) {
const IntegerValue slack =
new_head_lb - integer_trail_->UpperBound(arc.head_var) - 1;
integer_reason_.push_back(
integer_trail_->UpperBoundAsLiteral(arc.head_var));
std::vector<IntegerValue> coeffs(integer_reason_.size(), IntegerValue(1));
integer_trail_->RelaxLinearReason(slack, coeffs, &integer_reason_);
return integer_trail_->ReportConflict(literal_reason_, integer_reason_);
}
return integer_trail_->Enqueue(
IntegerLiteral::GreaterOrEqual(arc.head_var, new_head_lb),
literal_reason_, integer_reason_);
}
bool PrecedencesPropagator::NoPropagationLeft(const Trail& trail) const {
const int num_nodes = impacted_arcs_.size();
for (IntegerVariable var(0); var < num_nodes; ++var) {
for (const ArcIndex arc_index : impacted_arcs_[var]) {
const ArcInfo& arc = arcs_[arc_index];
if (integer_trail_->LowerBound(arc.tail_var) + ArcOffset(arc) >
integer_trail_->LowerBound(arc.head_var)) {
return false;
}
}
}
return true;
}
void PrecedencesPropagator::InitializeBFQueueWithModifiedNodes() {
// Sparse clear of the queue. TODO(user): only use the sparse version if
// queue.size() is small or use SparseBitset.
const int num_nodes = impacted_arcs_.size();
bf_in_queue_.resize(num_nodes, false);
for (const int node : bf_queue_) bf_in_queue_[node] = false;
bf_queue_.clear();
DCHECK(std::none_of(bf_in_queue_.begin(), bf_in_queue_.end(),
[](bool v) { return v; }));
for (const IntegerVariable var : modified_vars_.PositionsSetAtLeastOnce()) {
if (var >= num_nodes) continue;
bf_queue_.push_back(var.value());
bf_in_queue_[var.value()] = true;
}
}
void PrecedencesPropagator::CleanUpMarkedArcsAndParents() {
// To be sparse, we use the fact that each node with a parent must be in
// modified_vars_.
const int num_nodes = impacted_arcs_.size();
for (const IntegerVariable var : modified_vars_.PositionsSetAtLeastOnce()) {
if (var >= num_nodes) continue;
const ArcIndex parent_arc_index = bf_parent_arc_of_[var.value()];
if (parent_arc_index != -1) {
arcs_[parent_arc_index].is_marked = false;
bf_parent_arc_of_[var.value()] = -1;
bf_can_be_skipped_[var.value()] = false;
}
}
DCHECK(std::none_of(bf_parent_arc_of_.begin(), bf_parent_arc_of_.end(),
[](ArcIndex v) { return v != -1; }));
DCHECK(std::none_of(bf_can_be_skipped_.begin(), bf_can_be_skipped_.end(),
[](bool v) { return v; }));
}
bool PrecedencesPropagator::DisassembleSubtree(
int source, int target, std::vector<bool>* can_be_skipped) {
// Note that we explore a tree, so we can do it in any order, and the one
// below seems to be the fastest.
tmp_vector_.clear();
tmp_vector_.push_back(source);
while (!tmp_vector_.empty()) {
const int tail = tmp_vector_.back();
tmp_vector_.pop_back();
for (const ArcIndex arc_index : impacted_arcs_[IntegerVariable(tail)]) {
const ArcInfo& arc = arcs_[arc_index];
if (arc.is_marked) {
arc.is_marked = false; // mutable.
if (arc.head_var.value() == target) return true;
DCHECK(!(*can_be_skipped)[arc.head_var.value()]);
(*can_be_skipped)[arc.head_var.value()] = true;
tmp_vector_.push_back(arc.head_var.value());
}
}
}
return false;
}
void PrecedencesPropagator::AnalyzePositiveCycle(
ArcIndex first_arc, Trail* trail, std::vector<Literal>* must_be_all_true,
std::vector<Literal>* literal_reason,
std::vector<IntegerLiteral>* integer_reason) {
must_be_all_true->clear();
literal_reason->clear();
integer_reason->clear();
// Follow bf_parent_arc_of_[] to find the cycle containing first_arc.
const IntegerVariable first_arc_head = arcs_[first_arc].head_var;
ArcIndex arc_index = first_arc;
std::vector<ArcIndex> arc_on_cycle;
// Just to be safe and avoid an infinite loop we use the fact that the maximum
// cycle size on a graph with n nodes is of size n. If we have more in the
// code below, it means first_arc is not part of a cycle according to
// bf_parent_arc_of_[], which should never happen.
const int num_nodes = impacted_arcs_.size();
while (arc_on_cycle.size() <= num_nodes) {
arc_on_cycle.push_back(arc_index);
const ArcInfo& arc = arcs_[arc_index];
if (arc.tail_var == first_arc_head) break;
arc_index = bf_parent_arc_of_[arc.tail_var.value()];
CHECK_NE(arc_index, ArcIndex(-1));
}
CHECK_NE(arc_on_cycle.size(), num_nodes + 1) << "Infinite loop.";
// Compute the reason for this cycle.
IntegerValue sum(0);
for (const ArcIndex arc_index : arc_on_cycle) {
const ArcInfo& arc = arcs_[arc_index];
sum += ArcOffset(arc);
AppendLowerBoundReasonIfValid(arc.offset_var, *integer_trail_,
integer_reason);
for (const Literal l : arc.presence_literals) {
literal_reason->push_back(l.Negated());
}
}
// TODO(user): what if the sum overflow? this is just a check so I guess
// we don't really care, but fix the issue.
CHECK_GT(sum, 0);
}
// Note that in our settings it is important to use an algorithm that tries to
// minimize the number of integer_trail_->Enqueue() as much as possible.
//
// TODO(user): The current algorithm is quite efficient, but there is probably
// still room for improvements.
bool PrecedencesPropagator::BellmanFordTarjan(Trail* trail) {
const int num_nodes = impacted_arcs_.size();
// These vector are reset by CleanUpMarkedArcsAndParents() so resize is ok.
bf_can_be_skipped_.resize(num_nodes, false);
bf_parent_arc_of_.resize(num_nodes, ArcIndex(-1));
const auto cleanup =
::absl::MakeCleanup([this]() { CleanUpMarkedArcsAndParents(); });
// The queue initialization is done by InitializeBFQueueWithModifiedNodes().
while (!bf_queue_.empty()) {
const int node = bf_queue_.front();
bf_queue_.pop_front();
bf_in_queue_[node] = false;
// TODO(user): we don't need bf_can_be_skipped_ since we can detect this
// if this node has a parent arc which is not marked. Investigate if it is
// faster without the vector<bool>.
//
// TODO(user): An alternative algorithm is to remove all these nodes from
// the queue instead of simply marking them. This should also lead to a
// better "relaxation" order of the arcs. It is however a bit more work to
// remove them since we need to track their position.
if (bf_can_be_skipped_[node]) {
DCHECK_NE(bf_parent_arc_of_[node], -1);
DCHECK(!arcs_[bf_parent_arc_of_[node]].is_marked);
continue;
}
const IntegerValue tail_lb =
integer_trail_->LowerBound(IntegerVariable(node));
for (const ArcIndex arc_index : impacted_arcs_[IntegerVariable(node)]) {
const ArcInfo& arc = arcs_[arc_index];
DCHECK_EQ(arc.tail_var, node);
const IntegerValue candidate = tail_lb + ArcOffset(arc);
if (candidate > integer_trail_->LowerBound(arc.head_var)) {
if (!EnqueueAndCheck(arc, candidate, trail)) return false;
// This is the Tarjan contribution to Bellman-Ford. This code detect
// positive cycle, and because it disassemble the subtree while doing
// so, the cost is amortized during the algorithm execution. Another
// advantages is that it will mark the node explored here as skippable
// which will avoid to propagate them too early (knowing that they will
// need to be propagated again later).
if (DisassembleSubtree(arc.head_var.value(), arc.tail_var.value(),
&bf_can_be_skipped_)) {
std::vector<Literal> must_be_all_true;
AnalyzePositiveCycle(arc_index, trail, &must_be_all_true,
&literal_reason_, &integer_reason_);
if (must_be_all_true.empty()) {
++num_cycles_;
return integer_trail_->ReportConflict(literal_reason_,
integer_reason_);
} else {
gtl::STLSortAndRemoveDuplicates(&must_be_all_true);
for (const Literal l : must_be_all_true) {
if (trail_->Assignment().LiteralIsFalse(l)) {
literal_reason_.push_back(l);
return integer_trail_->ReportConflict(literal_reason_,
integer_reason_);
}
}
for (const Literal l : must_be_all_true) {
if (trail_->Assignment().LiteralIsTrue(l)) continue;
integer_trail_->EnqueueLiteral(l, literal_reason_,
integer_reason_);
}
// We just marked some optional variable as ignored, no need
// to update bf_parent_arc_of_[].
continue;
}
}
// We need to enforce the invariant that only the arc_index in
// bf_parent_arc_of_[] are marked (but not necessarily all of them
// since we unmark some in DisassembleSubtree()).
if (bf_parent_arc_of_[arc.head_var.value()] != -1) {
arcs_[bf_parent_arc_of_[arc.head_var.value()]].is_marked = false;
}
// Tricky: We just enqueued the fact that the lower-bound of head is
// candidate. However, because the domain of head may be discrete, it is
// possible that the lower-bound of head is now higher than candidate!
// If this is the case, we don't update bf_parent_arc_of_[] so that we
// don't wrongly detect a positive weight cycle because of this "extra
// push".
const IntegerValue new_bound = integer_trail_->LowerBound(arc.head_var);
if (new_bound == candidate) {
bf_parent_arc_of_[arc.head_var.value()] = arc_index;
arcs_[arc_index].is_marked = true;
} else {
// We still unmark any previous dependency, since we have pushed the
// value of arc.head_var further.
bf_parent_arc_of_[arc.head_var.value()] = -1;
}
// We do not re-enqueue if we are in a propagation loop and new_bound
// was not pushed to candidate or higher.
bf_can_be_skipped_[arc.head_var.value()] = false;
if (!bf_in_queue_[arc.head_var.value()] && new_bound >= candidate) {
bf_queue_.push_back(arc.head_var.value());
bf_in_queue_[arc.head_var.value()] = true;
}
}
}
}
return true;
}
void GreaterThanAtLeastOneOfDetector::Add(Literal lit, LinearTerm a,
LinearTerm b, IntegerValue lhs,
IntegerValue rhs) {
Relation r;
r.enforcement = lit;
r.a = a;
r.b = b;
r.lhs = lhs;
r.rhs = rhs;
// We shall only consider positive variable here.
if (r.a.var != kNoIntegerVariable && !VariableIsPositive(r.a.var)) {
r.a.var = NegationOf(r.a.var);
r.a.coeff = -r.a.coeff;
}
if (r.b.var != kNoIntegerVariable && !VariableIsPositive(r.b.var)) {
r.b.var = NegationOf(r.b.var);
r.b.coeff = -r.b.coeff;
}
relations_.push_back(std::move(r));
}
bool GreaterThanAtLeastOneOfDetector::AddRelationFromIndices(
IntegerVariable var, absl::Span<const Literal> clause,
absl::Span<const int> indices, Model* model) {
std::vector<AffineExpression> exprs;
std::vector<Literal> selectors;
absl::flat_hash_set<LiteralIndex> used;
auto* integer_trail = model->GetOrCreate<IntegerTrail>();
const IntegerValue var_lb = integer_trail->LevelZeroLowerBound(var);
for (const int index : indices) {
Relation r = relations_[index];
if (r.a.var != PositiveVariable(var)) std::swap(r.a, r.b);
CHECK_EQ(r.a.var, PositiveVariable(var));
if ((r.a.coeff == 1) == VariableIsPositive(var)) {
// a + b >= lhs
if (r.lhs <= kMinIntegerValue) continue;
exprs.push_back(AffineExpression(r.b.var, -r.b.coeff, r.lhs));
} else {
// -a + b <= rhs.
if (r.rhs >= kMaxIntegerValue) continue;
exprs.push_back(AffineExpression(r.b.var, r.b.coeff, -r.rhs));
}
// Ignore this entry if it is always true.
if (var_lb >= integer_trail->LevelZeroUpperBound(exprs.back())) {
exprs.pop_back();
continue;
}
// Note that duplicate selector are supported.
selectors.push_back(r.enforcement);
used.insert(r.enforcement);
}
// The enforcement of the new constraint are simply the literal not used
// above.
std::vector<Literal> enforcements;
for (const Literal l : clause) {
if (!used.contains(l.Index())) {
enforcements.push_back(l.Negated());
}
}
// No point adding a constraint if there is not at least two different
// literals in selectors.
if (used.size() <= 1) return false;
// Add the constraint.
GreaterThanAtLeastOneOfPropagator* constraint =
new GreaterThanAtLeastOneOfPropagator(var, exprs, selectors, enforcements,
model);
constraint->RegisterWith(model->GetOrCreate<GenericLiteralWatcher>());
model->TakeOwnership(constraint);
return true;
}
int GreaterThanAtLeastOneOfDetector::
AddGreaterThanAtLeastOneOfConstraintsFromClause(
const absl::Span<const Literal> clause, Model* model) {
CHECK_EQ(model->GetOrCreate<Trail>()->CurrentDecisionLevel(), 0);
if (clause.size() < 2) return 0;
// Collect all relations impacted by this clause.
std::vector<std::pair<IntegerVariable, int>> infos;
for (const Literal l : clause) {
if (l.Index() >= lit_to_relations_->size()) continue;
for (const int index : (*lit_to_relations_)[l.Index()]) {
const Relation& r = relations_[index];
if (r.a.var != kNoIntegerVariable && IntTypeAbs(r.a.coeff) == 1) {
infos.push_back({r.a.var, index});
}
if (r.b.var != kNoIntegerVariable && IntTypeAbs(r.b.coeff) == 1) {
infos.push_back({r.b.var, index});
}
}
}
if (infos.size() <= 1) return 0;
// Stable sort to regroup by var.
std::stable_sort(infos.begin(), infos.end());
// We process the info with same variable together.
int num_added_constraints = 0;
std::vector<int> indices;
for (int i = 0; i < infos.size();) {
const int start = i;
const IntegerVariable var = infos[start].first;
indices.clear();
for (; i < infos.size() && infos[i].first == var; ++i) {
indices.push_back(infos[i].second);
}
// Skip single relations, we are not interested in these.
if (indices.size() < 2) continue;
// Heuristic. Look for full or almost full clauses.
//
// TODO(user): We could add GreaterThanAtLeastOneOf() with more enforcement
// literals. Experiment.
if (indices.size() + 1 < clause.size()) continue;
if (AddRelationFromIndices(var, clause, indices, model)) {
++num_added_constraints;
}
if (AddRelationFromIndices(NegationOf(var), clause, indices, model)) {
++num_added_constraints;
}
}
return num_added_constraints;
}
int GreaterThanAtLeastOneOfDetector::
AddGreaterThanAtLeastOneOfConstraintsWithClauseAutoDetection(Model* model) {
auto* time_limit = model->GetOrCreate<TimeLimit>();
auto* solver = model->GetOrCreate<SatSolver>();
// Fill the set of interesting relations for each variables.
util_intops::StrongVector<IntegerVariable, std::vector<int>> var_to_relations;
for (int index = 0; index < relations_.size(); ++index) {
const Relation& r = relations_[index];
if (r.a.var != kNoIntegerVariable && IntTypeAbs(r.a.coeff) == 1) {
if (r.a.var >= var_to_relations.size()) {
var_to_relations.resize(r.a.var + 1);
}
var_to_relations[r.a.var].push_back(index);
}
if (r.b.var != kNoIntegerVariable && IntTypeAbs(r.b.coeff) == 1) {
if (r.b.var >= var_to_relations.size()) {
var_to_relations.resize(r.b.var + 1);
}
var_to_relations[r.b.var].push_back(index);
}
}
int num_added_constraints = 0;
for (IntegerVariable target(0); target < var_to_relations.size(); ++target) {
if (var_to_relations[target].size() <= 1) continue;
if (time_limit->LimitReached()) return num_added_constraints;
// Detect set of incoming arcs for which at least one must be present.
// TODO(user): Find more than one disjoint set of incoming arcs.
// TODO(user): call MinimizeCoreWithPropagation() on the clause.
solver->Backtrack(0);
if (solver->ModelIsUnsat()) return num_added_constraints;
std::vector<Literal> clause;
for (const int index : var_to_relations[target]) {
const Literal literal = relations_[index].enforcement;
if (solver->Assignment().LiteralIsFalse(literal)) continue;
const SatSolver::Status status =
solver->EnqueueDecisionAndBacktrackOnConflict(literal.Negated());
if (status == SatSolver::INFEASIBLE) return num_added_constraints;
if (status == SatSolver::ASSUMPTIONS_UNSAT) {
// We need to invert it, since a clause is not all false.
clause = solver->GetLastIncompatibleDecisions();
for (Literal& ref : clause) ref = ref.Negated();
break;
}
}
solver->Backtrack(0);
if (clause.size() <= 1) continue;
// Recover the indices corresponding to this clause.
const absl::btree_set<Literal> clause_set(clause.begin(), clause.end());
std::vector<int> indices;
for (const int index : var_to_relations[target]) {
const Literal literal = relations_[index].enforcement;
if (clause_set.contains(literal)) {
indices.push_back(index);
}
}
// Try both direction.
if (AddRelationFromIndices(target, clause, indices, model)) {
++num_added_constraints;
}
if (AddRelationFromIndices(NegationOf(target), clause, indices, model)) {
++num_added_constraints;
}
}
solver->Backtrack(0);
return num_added_constraints;
}
int GreaterThanAtLeastOneOfDetector::AddGreaterThanAtLeastOneOfConstraints(
Model* model, bool auto_detect_clauses) {
auto* time_limit = model->GetOrCreate<TimeLimit>();
auto* solver = model->GetOrCreate<SatSolver>();
auto* clauses = model->GetOrCreate<ClauseManager>();
auto* logger = model->GetOrCreate<SolverLogger>();
int num_added_constraints = 0;
SOLVER_LOG(logger, "[Precedences] num_relations=", relations_.size(),
" num_clauses=", clauses->AllClausesInCreationOrder().size());
// Initialize lit_to_relations_.
{
std::vector<LiteralIndex> keys;
const int num_relations = relations_.size();
keys.reserve(num_relations);
for (int i = 0; i < num_relations; ++i) {
keys.push_back(relations_[i].enforcement.Index());
}
lit_to_relations_ =
std::make_unique<CompactVectorVector<LiteralIndex, int>>();
lit_to_relations_->ResetFromFlatMapping(keys, IdentityMap<int>());
}
// We have two possible approaches. For now, we prefer the first one except if
// there is too many clauses in the problem.
//
// TODO(user): Do more extensive experiment. Remove the second approach as
// it is more time consuming? or identify when it make sense. Note that the
// first approach also allows to use "incomplete" at least one between arcs.
if (!auto_detect_clauses &&
clauses->AllClausesInCreationOrder().size() < 1e6) {
// TODO(user): This does not take into account clause of size 2 since they
// are stored in the BinaryImplicationGraph instead. Some ideas specific
// to size 2:
// - There can be a lot of such clauses, but it might be nice to consider
// them. we need to experiments.
// - The automatic clause detection might be a better approach and it
// could be combined with probing.
for (const SatClause* clause : clauses->AllClausesInCreationOrder()) {
if (time_limit->LimitReached()) return num_added_constraints;
if (solver->ModelIsUnsat()) return num_added_constraints;
num_added_constraints += AddGreaterThanAtLeastOneOfConstraintsFromClause(
clause->AsSpan(), model);
}
// It is common that there is only two alternatives to push a variable.
// In this case, our presolve most likely made sure that the two are
// controlled by a single Boolean. This allows to detect this and add the
// appropriate greater than at least one of.
const int num_booleans = solver->NumVariables();
if (num_booleans < 1e6) {
for (int i = 0; i < num_booleans; ++i) {
if (time_limit->LimitReached()) return num_added_constraints;
if (solver->ModelIsUnsat()) return num_added_constraints;
num_added_constraints +=
AddGreaterThanAtLeastOneOfConstraintsFromClause(
{Literal(BooleanVariable(i), true),
Literal(BooleanVariable(i), false)},
model);
}
}
} else {
num_added_constraints +=
AddGreaterThanAtLeastOneOfConstraintsWithClauseAutoDetection(model);
}
if (num_added_constraints > 0) {
SOLVER_LOG(logger, "[Precedences] Added ", num_added_constraints,
" GreaterThanAtLeastOneOf() constraints.");
}
// Release the memory, it is not longer needed.
lit_to_relations_.reset(nullptr);
gtl::STLClearObject(&relations_);
return num_added_constraints;
}
} // namespace sat
} // namespace operations_research
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