100 lines
3.3 KiB
Go
100 lines
3.3 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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// The step_function_sample_sat command is an example of an implementation of a step function.
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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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cmpb "github.com/google/or-tools/ortools/sat/proto/cpmodel"
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sppb "github.com/google/or-tools/ortools/sat/proto/satparameters"
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"google.golang.org/protobuf/proto"
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)
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func stepFunctionSampleSat() error {
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// Create the CP-SAT model.
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model := cpmodel.NewCpModelBuilder()
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// Declare our primary variable.
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x := model.NewIntVar(0, 20)
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// Create the expression variable and implement the step function
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// Note it is not defined for var == 2.
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//
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// - 3
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// -- -- --------- 2
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// 1
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// -- --- 0
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// 1 2
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// 012345678901234567890
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//
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expr := model.NewIntVar(0, 3)
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// expr == 0 on [5, 6] U [8, 10]
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b0 := model.NewBoolVar()
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d0 := cpmodel.FromValues([]int64{5, 6, 8, 9, 10})
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model.AddLinearConstraintForDomain(x, d0).OnlyEnforceIf(b0)
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model.AddEquality(expr, cpmodel.NewConstant(0)).OnlyEnforceIf(b0)
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// expr == 2 on [0, 1] U [3, 4] U [11, 20]
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b2 := model.NewBoolVar()
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d2 := cpmodel.FromIntervals([]cpmodel.ClosedInterval{{Start: 0, End: 1}, {Start: 3, End: 4}, {Start: 11, End: 20}})
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model.AddLinearConstraintForDomain(x, d2).OnlyEnforceIf(b2)
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model.AddEquality(expr, cpmodel.NewConstant(2)).OnlyEnforceIf(b2)
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// expr = 3 when x = 7
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b3 := model.NewBoolVar()
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model.AddEquality(x, cpmodel.NewConstant(7)).OnlyEnforceIf(b3)
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model.AddEquality(expr, cpmodel.NewConstant(3)).OnlyEnforceIf(b3)
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// At least one Boolean variable is true.
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model.AddBoolOr(b0, b2, b3)
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// Search for x values in increasing order.
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model.AddDecisionStrategy([]cpmodel.IntVar{x}, cmpb.DecisionStrategyProto_CHOOSE_FIRST, cmpb.DecisionStrategyProto_SELECT_MIN_VALUE)
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// Create a solver and solve with fixed search.
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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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params := &sppb.SatParameters{
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FillAdditionalSolutionsInResponse: proto.Bool(true),
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EnumerateAllSolutions: proto.Bool(true),
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SolutionPoolSize: proto.Int32(21),
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SearchBranching: sppb.SatParameters_FIXED_SEARCH.Enum(),
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}
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response, err := cpmodel.SolveCpModelWithParameters(m, params)
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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.Printf("Status: %v\n", response.GetStatus())
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for _, additionalSolution := range response.GetAdditionalSolutions() {
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vs := additionalSolution.GetValues()
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fmt.Printf("x= %v expr= %v\n", vs[x.Index()], vs[expr.Index()])
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}
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return nil
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}
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func main() {
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if err := stepFunctionSampleSat(); err != nil {
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log.Exitf("stepFunctionSampleSat returned with error: %v", err)
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}
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}
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