source: branches/2936_GQAPIntegration/HeuristicLab.Problems.GeneralizedQuadraticAssignment/3.3/SolutionCreators/RandomButFeasibleSolutionCreator.cs @ 16712

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
 *
 * This file is part of HeuristicLab.
 *
 * HeuristicLab is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
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 * GNU General Public License for more details.
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#endregion

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Data;
using HeuristicLab.Encodings.IntegerVectorEncoding;
using HeuristicLab.Parameters;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
using HeuristicLab.Random;
using HEAL.Attic;

namespace HeuristicLab.Problems.GeneralizedQuadraticAssignment {
  [Item("RandomButFeasibleSolutionCreator", "Creates a random, but feasible solution to the Generalized Quadratic Assignment Problem.")]
  [StorableType("3C194DAF-81A9-4FA3-AE7F-45951FC33DE1")]
  public class RandomFeasibleSolutionCreator : GQAPStochasticSolutionCreator {

    public IValueLookupParameter<IntValue> MaximumTriesParameter {
      get { return (IValueLookupParameter<IntValue>)Parameters["MaximumTries"]; }
    }
    public IValueLookupParameter<BoolValue> CreateMostFeasibleSolutionParameter {
      get { return (IValueLookupParameter<BoolValue>)Parameters["CreateMostFeasibleSolution"]; }
    }

    [StorableConstructor]
    protected RandomFeasibleSolutionCreator(StorableConstructorFlag _) : base(_) { }
    protected RandomFeasibleSolutionCreator(RandomFeasibleSolutionCreator original, Cloner cloner) : base(original, cloner) { }
    public RandomFeasibleSolutionCreator()
      : base() {
      Parameters.Add(new ValueLookupParameter<IntValue>("MaximumTries", "The maximum number of tries to create a feasible solution after which an exception is thrown. If it is set to 0 or a negative value there will be an infinite number of attempts.", new IntValue(100000)));
      Parameters.Add(new ValueLookupParameter<BoolValue>("CreateMostFeasibleSolution", "If this is set to true the operator will always succeed, and outputs the solution with the least violation instead of throwing an exception.", new BoolValue(false)));
    }

    public override IDeepCloneable Clone(Cloner cloner) {
      return new RandomFeasibleSolutionCreator(this, cloner);
    }

    public static IntegerVector CreateSolution(IRandom random, GQAPInstance problemInstance,
      int maximumTries, bool createMostFeasibleSolution, CancellationToken cancel) {
      var capacities = problemInstance.Capacities;
      var demands = problemInstance.Demands;
      IntegerVector result = null;
      bool isFeasible = false;
      int counter = 0;
      double minViolation = double.MaxValue;
      var slack = new double[capacities.Length];
      var assignment = new int[demands.Length];

      while (!isFeasible) {
        cancel.ThrowIfCancellationRequested();
        if (maximumTries > 0) {
          counter++;
          if (counter > maximumTries) {
            if (createMostFeasibleSolution) break;
            else throw new InvalidOperationException("A feasible solution could not be obtained after " + maximumTries + " attempts.");
          }
        }
        for (int i = 0; i < capacities.Length; i++) slack[i] = capacities[i];
        foreach (var equipment in Enumerable.Range(0, demands.Length).Shuffle(random)) {
          var freeLocations = GetFreeLocations(equipment, demands, slack);
          assignment[equipment] = freeLocations.SampleRandom(random);
          slack[assignment[equipment]] -= demands[equipment];
        }
        double violation = slack.Select(x => x < 0 ? -x : 0).Sum();
        isFeasible = violation == 0;
        if (isFeasible || violation < minViolation) {
          result = new IntegerVector(assignment);
          minViolation = violation;
        }
      }
      return result;
    }

    protected override IntegerVector CreateRandomSolution(IRandom random, GQAPInstance problemInstance) {
      return CreateSolution(random, problemInstance,
        MaximumTriesParameter.ActualValue.Value,
        CreateMostFeasibleSolutionParameter.ActualValue.Value,
        CancellationToken);
    }

    private static IEnumerable<int> GetFreeLocations(int equipment, DoubleArray demands, double[] freeCapacities) {
      var freeLocations = freeCapacities
        .Select((v, idx) => new KeyValuePair<int, double>(idx, v))
        .Where(x => x.Value >= demands[equipment]);
      if (!freeLocations.Any()) {
        freeLocations = freeCapacities
          .Select((v, idx) => new KeyValuePair<int, double>(idx, v))
          .OrderByDescending(x => x.Value)
          .Take(3); // if there are none, take the three where the free capacity is largest
      }
      return freeLocations.Select(x => x.Key);
    }
  }
}