public IEnumerable<int> FindRandomDisjointTour(IntegerPermutation otherTour)
{
this.InitializeVisit();
this.tabuEdgeList = TabuEdgeCollection.CreateFromTour(otherTour);
var randomEdge = this.GetRandomEdge();
while (tabuEdgeList.IsTabu(randomEdge))
randomEdge = this.GetRandomEdge();
this.VisitNode(randomEdge.Head);
yield return randomEdge.Head;
this.VisitNode(randomEdge.Tail);
yield return randomEdge.Tail;
int currentNode = randomEdge.Tail;
TaskLogger.Text = "Computing greedy and tabu search to generate a disjoint tour...";
while (unvisitedNodes.ItemsCount > 0)
{
int nearestUnvisitedNode = this.FindNearestUnvisitedNonTabuNode(currentNode);
this.VisitNode(nearestUnvisitedNode);
yield return nearestUnvisitedNode;
currentNode = nearestUnvisitedNode;
TaskLogger.Progress = 100.0 * visitedNodes.ItemsCount / nodes.Length;
}
}
public static TabuEdgeCollection CreateFromTour(IntegerPermutation otherTour)
{
var result = new TabuEdgeCollection();
result.tabuDirectArcs = new int[otherTour.Length];
result.tabuReverseArcs = new int[otherTour.Length];
int upperBound = otherTour.Length - 1;
for (int i = 0; i < upperBound; i++)
{
int head = otherTour[i];
int tail = otherTour[i + 1];
result.tabuDirectArcs[head] = tail;
result.tabuReverseArcs[tail] = head;
}
result.tabuDirectArcs[otherTour[upperBound]] = otherTour[0];
result.tabuReverseArcs[otherTour[0]] = otherTour[upperBound];
return result;
}
public void CrossOptimize(IntegerPermutation solution, IntegerPermutation betterSolution)
{
var tabuList = TabuEdgeCollection.CreateFromTour(betterSolution);
var currentDistance = nodes.GetDistance(solution);
var betterDistance = nodes.GetDistance(betterSolution);
int end = nodes.Length - 1;
this.currentSolution = solution;
this.betterSolution = betterSolution;
this.tabuList = tabuList;
double overallGain = 0, overallCost = 0;
TaskLogger.Text = "Running cross 2-opt heuristic on both solutions...";
for (int i = 0; i < end; i++)
{
for (int j = i + 2; j < end; j++)
{
int a = solution[i];
int b = solution[i + 1];
int c = solution[j];
int d = solution[j + 1];
bool acTabu = tabuList.IsTabu(a, c);
bool bdTabu = tabuList.IsTabu(b, d);
// Only one edge can be swapped between solution, otherwise it's a mess
if (acTabu && bdTabu)
continue;
var acDistance = nodes.GetDistance(a, c);
var bdDistance = nodes.GetDistance(b, d);
var abDistance = nodes.GetDistance(a, b);
var cdDistance = nodes.GetDistance(c, d);
bool improvable = (acDistance + bdDistance < abDistance + cdDistance);
// If the solution cannot be improved, skip this
if (!improvable)
continue;
// If target edge switches are not prohibited, proceed as usual
if (!acTabu && !bdTabu)
{
solution.ReverseSubsequence(i + 1, j);
}
else
{
int startNode, middleNode, endNode;
double delta = 0;
if (acTabu)
{
startNode = a;
endNode = c;
middleNode = this.FindTwoEdgesPathMiddleNode(a, c);
delta = this.ComputeCostOfTraversing(a, middleNode, c);
}
else // if (bdTabu)
{
startNode = b;
endNode = d;
middleNode = this.FindTwoEdgesPathMiddleNode(b, d);
delta = this.ComputeCostOfTraversing(b, middleNode, d);
}
// Increase in distance of the best solution
var cost = delta;
// Decerase in distance of the second solution
var gain = (abDistance + cdDistance) - (acDistance + bdDistance);
if ((gain > 0) && (gain > cost))
{
var newBetterDistance = betterDistance + cost;
var newCurrentDistance = currentDistance - gain;
// By performing this move, the solution would be worse, so end here
if (newBetterDistance > newCurrentDistance)
return;
solution.ReverseSubsequence(i + 1, j);
int destinationIndex = betterSolution.IndexOf(endNode);
betterSolution.MoveBefore(middleNode, destinationIndex);
betterDistance = newBetterDistance;
currentDistance = newCurrentDistance;
overallGain += gain;
overallCost += cost;
TaskLogger.Text = String.Format("Overall gain: {0:N0}, Overall cost: {1:N0}", overallGain, overallCost);
}
}
}
TaskLogger.Progress = 100.0 * i / end;
}
}