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improve binpacking_2d_sat.cc example

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Laurent Perron
2022-01-08 14:45:54 +01:00
parent 6f5643a07f
commit 58a32b0510
1 changed files with 43 additions and 33 deletions
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76
examples/cpp/binpacking_2d_sat.cc
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@@ -38,10 +38,12 @@ 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,
ABSL_FLAG(bool, symmetry_breaking, true,
"Use the advanced symmetry breaking constraints");
ABSL_FLAG(bool, global_area_constraint, false,
"Redundant constraint to link the global area covered");
ABSL_FLAG(bool, alternate_model, true,
"A different way to express the objective");
namespace operations_research {
namespace sat {
@@ -153,44 +155,52 @@ void LoadAndSolve(const std::string& file_name, int instance) {
cp_model.AddEquality(sum_of_areas, sum_of_items_area);
}
// 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();
// Link bin_is_used[i] with the items in bin i.
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]);
}
cp_model.AddBoolOr(all_items_in_bin).OnlyEnforceIf(bin_is_used[b]);
}
// 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;
if (absl::GetFlag(FLAGS_alternate_model)) {
const IntVar obj = cp_model.NewIntVar(Domain(trivial_lb, max_bins));
cp_model.Minimize(obj);
for (int b = trivial_lb; b < max_bins; ++b) {
for (int item = 0; item < num_items; ++item) {
items_in_bins.push_back(item_to_bin[item][b]);
cp_model.AddGreaterOrEqual(obj, b + 1)
.OnlyEnforceIf(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]);
// 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();
// Link bin_is_used[i] with the items in bin i.
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]);
}
cp_model.AddBoolOr(all_items_in_bin).OnlyEnforceIf(bin_is_used[b]);
}
}
// Objective.
cp_model.Minimize(LinearExpr::Sum(bin_is_used));
// Symmetry breaking.
if (absl::GetFlag(FLAGS_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]);
}
}
// Objective.
cp_model.Minimize(LinearExpr::Sum(bin_is_used));
}
// Setup parameters.
SatParameters parameters;