volsay2.cs

// Copyright 2012 Hakan Kjellerstrand
//
// 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.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using Google.OrTools.LinearSolver;

public class Volsay2 {
  /**
   * Volsay problem.
   *
   * From the OPL model volsay.mod.
   *
   * Also see
   *  http://www.hakank.org/or-tools/volsay.cs
   *  http://www.hakank.org/or-tools/volsay2.py
   */
  private static void Solve() {
    Solver solver = new Solver(
    	   "Volsay2", Solver.OptimizationProblemType.CLP_LINEAR_PROGRAMMING);

    int num_products = 2;
    IEnumerable<int> PRODUCTS = Enumerable.Range(0, num_products);
    int Gas = 0;
    int Chloride = 1;
    String[] products = {"Gas", "Chloride"};

    //
    // Variables
    //
    Variable[] production = new Variable[num_products];
    foreach(int p in PRODUCTS) {
      production[p] = solver.MakeNumVar(0, 100000, products[p]);
    }

    int num_constraints = 2;
    IEnumerable<int> CONSTRAINTS = Enumerable.Range(0, num_constraints);
    Constraint[] cons = new Constraint[num_constraints];
    cons[0] = solver.Add(production[Gas] + production[Chloride] <= 50);
    cons[1] = solver.Add(3 * production[Gas] + 4 * production[Chloride] <= 180);

    solver.Maximize(40 * production[Gas] + 50 * production[Chloride]);

    Console.WriteLine("NumConstraints: {0}", solver.NumConstraints());

    Solver.ResultStatus resultStatus = solver.Solve();

    if (resultStatus != Solver.ResultStatus.OPTIMAL) {
      Console.WriteLine("The problem don't have an optimal solution.");
      return;
    }

    foreach(int p in PRODUCTS) {
      Console.WriteLine("{0,-10}: {1} ReducedCost: {2}",
                        products[p],
                        production[p].SolutionValue(),
                        production[p].ReducedCost());
    }

    double[] activities = solver.ComputeConstraintActivities();
    foreach(int c in CONSTRAINTS) {
      Console.WriteLine(
          "Constraint {0} DualValue {1} Activity: {2} lb: {3} ub: {4}",
          c.ToString(),
          cons[c].DualValue(),
          activities[cons[c].Index()],
          cons[c].Lb(),
          cons[c].Ub());
    }

    Console.WriteLine("\nWallTime: " + solver.WallTime());
    Console.WriteLine("Iterations: " + solver.Iterations());

  }

  public static void Main(String[] args) {
    Solve();
  }
}