/// <summary>
/// Perform an operation on the current solution.
/// </summary>
/// <param name="operation">The local search operation to be performed.</param>
/// <returns>If the operation improved the best known upper bound on the cost.</returns>
public virtual bool PerformOperation(LocalSearchOperation operation)
{
this.PerformedOperations.Add(operation);
operation.Execute();
if (this.CurrentSolution.Cost < this.BestCost)
{
this.BestCost = this.CurrentSolution.Cost;
this.BestWidth = this.CurrentSolution.Width;
return(true);
}
return(false);
}
/// <summary>
/// Perform a single iteration of the local search.
/// </summary>
/// <returns>Should the search continue?</returns>
protected virtual bool PerformIteration()
{
LocalSearchOperation candidate = this.GetCandidate();
if (candidate == null)
{
return(false);
}
this.focus.PerformOperation(candidate);
this.UpdateFocus();
Console.WriteLine($"{this.focus.CurrentSolution.Width.ToString("N2")} {this.focus.CurrentSolution.Cost.ToString("N0")}");
return(true);
}
protected override LocalSearchOperation GetCandidate()
{
LocalSearchOperation candidate = null;
double cost = this.cost;
foreach (var op in this.operators)
{
foreach (var operation in op.Operations(this.focus.CurrentSolution, this.randomNumberGenerator))
{
this.ExploredSolutions++;
if (operation.Cost - cost < -PRECISION)
{
candidate = operation;
cost = candidate.Cost;
}
}
}
return(candidate);
}
protected override bool PerformIteration()
{
if (this.CurrentComputationTime - this.previousCooling > this.Q)
{
this.previousCooling = this.CurrentComputationTime;
this.T *= ALPHA;
}
LocalSearchOperation candidate = this.GetCandidate();
if (candidate.Cost < this.focus.CurrentSolution.Cost)
{
if (candidate.Cost < this.focus.BestCost)
{
this.iterationsWithoutImprovement = 0;
Console.WriteLine($"{this.CurrentComputationTime.ToString("N0")}: {this.focus.BestWidth.ToString("N2")} {candidate.Cost.ToString("N0")} | T={this.T.ToString("N2")}");
}
this.focus.PerformOperation(candidate);
var focus = this.focus;
if (focus != this.UpdateFocus())
{
this.Q = this.computeCoolingInterval(this.T, this.targetT, (int)(this.MaximumComputationTime - this.CurrentComputationTime));
}
//Console.WriteLine($"{this.CurrentComputationTime.ToString("N0")}: {this.focus.CurrentSolution.Width.ToString("N2")} {this.focus.CurrentSolution.Cost.ToString("N0")} | T={this.T.ToString("N2")}");
}
else
{
if (++this.iterationsWithoutImprovement > this.FailedIterationsUntilReset)
{
this.focus.Revert();
this.iterationsWithoutImprovement = 0;
Console.WriteLine($"Reset");
}
else if (this.acceptDeterioration(candidate.Cost - this.focus.CurrentSolution.Cost, this.T))
{
//Console.WriteLine($"Accepted deterioration of size {(candidate.Cost - this.focus.CurrentSolution.Cost).ToString("N0")}, rejection {this.iterationsWithoutImprovement}");
this.focus.PerformOperation(candidate);
}
}
return(true);
}
protected override bool PerformIteration()
{
LocalSearchOperation candidate = this.GetCandidate();
// If no better neighbor is found
if (candidate == null)
{
// Revert to the best solution so far.
// Note: reverting is not necessary, it might be better to remove it.
Console.WriteLine($"Perturbation of size {this.CurrentPerturbationSize} after {this.Failures + 1} failures; best = {this.focus.BestCost.ToString("F2")}");
if (this.focus.CurrentSolution.Cost > this.focus.BestCost)
{
this.focus.Revert();
}
// Perturb the solution by taking a number of random steps.
for (int i = 0; i < this.CurrentPerturbationSize; i++)
{
LocalSearchOperation operation = this.operators[this.randomNumberGenerator.Next(this.operators.Length)].GetRandomOperation(this.focus.CurrentSolution, this.randomNumberGenerator);
this.focus.PerformOperation(operation);
}
Console.WriteLine($"Result of perturbation: {this.focus.CurrentSolution.Width.ToString("F2")} {this.focus.CurrentSolution.Cost.ToString("F0")}");
this.Failures++;
}
else
{
if (this.focus.PerformOperation(candidate))
{
this.Failures = 0;
}
this.UpdateFocus();
Console.WriteLine($"{this.focus.CurrentSolution.Width.ToString("F2")} {this.focus.CurrentSolution.Cost.ToString("F0")}");
}
return(true);
}
