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fix binpacking_2d_sat model

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Laurent Perron
2021-12-30 18:59:09 +01:00
parent 2b2ca9877a
commit 0a822872ed
1 changed files with 41 additions and 19 deletions
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60
examples/cpp/binpacking_2d_sat.cc
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@@ -38,6 +38,10 @@ ABSL_FLAG(std::string, params, "", "Sat parameters in text proto format.");
ABSL_FLAG(int, max_bins, 0,
"Maximum number of bins. The 0 default value implies the code will "
"use some heuristics to compute this number.");
ABSL_FLAG(bool, advanced_symmetry_breaking, true,
"Use the advanced symmetry breaking constraints");
ABSL_FLAG(bool, global_area_constraint, false,
"Redundant constraint to link the global area covered");
namespace operations_research {
namespace sat {
@@ -136,28 +140,21 @@ void LoadAndSolve(const std::string& file_name, int instance) {
}
// Redundant constraint.
LinearExpr sum_of_areas;
for (int item = 0; item < num_items; ++item) {
const int64_t item_area = problem.items(item).shapes(0).dimensions(0) *
problem.items(item).shapes(0).dimensions(1);
for (int b = 0; b < max_bins; ++b) {
sum_of_areas += item_to_bin[item][b] * item_area;
}
}
cp_model.AddEquality(sum_of_areas, sum_of_items_area);
// Symmetry breaking: The number of items per bin is decreasing.
std::vector<LinearExpr> num_items_in_bin(max_bins);
for (int b = 0; b < max_bins; ++b) {
// The sum of areas in each bin is the sum of all items area.
if (absl::GetFlag(FLAGS_global_area_constraint)) {
LinearExpr sum_of_areas;
for (int item = 0; item < num_items; ++item) {
num_items_in_bin[b] += item_to_bin[item][b];
const int64_t item_area = problem.items(item).shapes(0).dimensions(0) *
problem.items(item).shapes(0).dimensions(1);
for (int b = 0; b < max_bins; ++b) {
sum_of_areas += item_to_bin[item][b] * item_area;
}
}
}
for (int b = 1; b < max_bins; ++b) {
cp_model.AddLessOrEqual(num_items_in_bin[b - 1], num_items_in_bin[b]);
cp_model.AddEquality(sum_of_areas, sum_of_items_area);
}
// Objective.
// Maintain one Boolean variable per bin that indicates if the bin is used or
// not.
std::vector<BoolVar> bin_is_used(max_bins);
for (int b = 0; b < max_bins; ++b) {
bin_is_used[b] = cp_model.NewBoolVar();
@@ -165,16 +162,41 @@ void LoadAndSolve(const std::string& file_name, int instance) {
std::vector<BoolVar> all_items_in_bin;
for (int item = 0; item < num_items; ++item) {
cp_model.AddImplication(item_to_bin[item][b], bin_is_used[b]);
all_items_in_bin.push_back(item_to_bin[item][b].Not());
all_items_in_bin.push_back(item_to_bin[item][b]);
}
all_items_in_bin.push_back(bin_is_used[b].Not());
cp_model.AddBoolOr(all_items_in_bin);
}
// Symmetry breaking.
if (absl::GetFlag(FLAGS_advanced_symmetry_breaking)) {
// Forces the number of items per bin to decrease.
std::vector<IntVar> num_items_in_bin(max_bins);
for (int b = 0; b < max_bins; ++b) {
num_items_in_bin[b] = cp_model.NewIntVar({0, num_items});
std::vector<BoolVar> items_in_bins;
for (int item = 0; item < num_items; ++item) {
items_in_bins.push_back(item_to_bin[item][b]);
}
cp_model.AddEquality(num_items_in_bin[b], LinearExpr::Sum(items_in_bins));
}
for (int b = 1; b < max_bins; ++b) {
cp_model.AddGreaterOrEqual(num_items_in_bin[b - 1], num_items_in_bin[b]);
}
} else {
// Forces used bins to be continuous starting at 0.
for (int b = 1; b < max_bins; ++b) {
cp_model.AddImplication(bin_is_used[b], bin_is_used[b - 1]);
}
}
// Objective.
cp_model.Minimize(LinearExpr::Sum(bin_is_used));
// Setup parameters.
SatParameters parameters;
parameters.set_log_search_progress(true);
parameters.set_use_cumulative_in_no_overlap_2d(true);
// Parse the --params flag.
if (!absl::GetFlag(FLAGS_params).empty()) {
CHECK(google::protobuf::TextFormat::MergeFromString(