4f381f6d07
* bump abseil to 20250814 * bump protobuf to v32.0 * cmake: add ccache auto support * backport flatzinc, math_opt and sat update
125 lines
3.2 KiB
Go
125 lines
3.2 KiB
Go
// Copyright 2010-2025 Google LLC
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// [START program]
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// The binpacking_problem_sat command is an example of a bin packing problem that uses channeling
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// constraints.
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package main
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import (
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"fmt"
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log "github.com/golang/glog"
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"github.com/google/or-tools/ortools/sat/go/cpmodel"
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)
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const (
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binCapacity = 100
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slackCapacity = 20
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safeCapacity = binCapacity - slackCapacity
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numBins = 5
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)
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type item struct {
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Cost, Copies int64
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}
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func binpackingProblemSat() error {
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// Create the CP-SAT model.
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model := cpmodel.NewCpModelBuilder()
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items := []item{{20, 6}, {15, 6}, {30, 4}, {45, 3}}
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numItems := len(items)
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// Main variables.
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x := make([][]cpmodel.IntVar, numItems)
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for i, item := range items {
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x[i] = make([]cpmodel.IntVar, numBins)
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for b := 0; b < numBins; b++ {
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x[i][b] = model.NewIntVar(0, item.Copies)
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}
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}
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// Load variables.
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load := make([]cpmodel.IntVar, numBins)
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for b := 0; b < numBins; b++ {
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load[b] = model.NewIntVar(0, binCapacity)
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}
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// Slack variables.
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slacks := make([]cpmodel.BoolVar, numBins)
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for b := 0; b < numBins; b++ {
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slacks[b] = model.NewBoolVar()
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}
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// Links load and x.
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for b := 0; b < numBins; b++ {
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expr := cpmodel.NewLinearExpr()
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for i := 0; i < numItems; i++ {
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expr.AddTerm(x[i][b], items[i].Cost)
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}
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model.AddEquality(expr, load[b])
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}
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// Place all items.
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for i := 0; i < numItems; i++ {
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copies := cpmodel.NewLinearExpr()
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for _, b := range x[i] {
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copies.Add(b)
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}
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model.AddEquality(copies, cpmodel.NewConstant(items[i].Copies))
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}
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// Links load and slack through an equivalence relation.
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for b := 0; b < numBins; b++ {
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// slacks[b] => load[b] <= safeCapacity.
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model.AddLessOrEqual(load[b], cpmodel.NewConstant(safeCapacity)).OnlyEnforceIf(slacks[b])
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// slacks[b].Not() => load[b] > safeCapacity.
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model.AddGreaterThan(load[b], cpmodel.NewConstant(safeCapacity)).OnlyEnforceIf(slacks[b].Not())
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}
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// Maximize sum of slacks.
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obj := cpmodel.NewLinearExpr()
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for _, s := range slacks {
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obj.Add(s)
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}
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model.Maximize(obj)
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// Solve.
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m, err := model.Model()
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if err != nil {
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return fmt.Errorf("failed to instantiate the CP model: %w", err)
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}
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response, err := cpmodel.SolveCpModel(m)
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if err != nil {
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return fmt.Errorf("failed to solve the model: %w", err)
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}
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fmt.Println("Status: ", response.GetStatus())
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fmt.Println("Objective: ", response.GetObjectiveValue())
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fmt.Println("Statistics: ")
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fmt.Println(" - conflicts : ", response.GetNumConflicts())
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fmt.Println(" - branches : ", response.GetNumBranches())
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fmt.Println(" - wall time : ", response.GetWallTime())
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return nil
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}
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func main() {
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if err := binpackingProblemSat(); err != nil {
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log.Exitf("binpackingProblemSat returned with error: %v", err)
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}
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}
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// [END program]
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