private void printRoute(BBNode node)
{
List<City> cities = new List<City>(Cities);
Console.WriteLine("Route: ");
foreach (Object obj in node.Route)
{
City city = (City)obj;
Console.Write(cities.IndexOf(city) + "->");
}
Console.WriteLine(cities.IndexOf((City)node.Route[0]));
}
/// <summary>
/// performs a Branch and Bound search of the state space of partial tours
/// stops when time limit expires and uses BSSF as solution
/// </summary>
/// <returns>results array for GUI that contains three ints: cost of solution, time spent to find solution, number of solutions found during search (not counting initial BSSF estimate)</returns>
public string[] bBSolveProblem()
{
string[] results = new string[3];
Stopwatch timer = new Stopwatch();
int intermediateSolutions = 0;
int numStatesCreated = 0;
int maxInQueue = 0;
int numStatesPruned = 0;
defaultSolveProblem();
timer.Start();
// initialize the root node
List<int> children = new List<int>();
int[,] matrix = initializeCostMatrix(Cities, ref children, 0);
//printMatrix(matrix, "Absolute Cost:");
BBNode rootNode = new BBNode(children, matrix, 0); // 0 is it's row index in the cost matrix
rootNode.reduceMatrix();
//printMatrix(rootNode.costMatrix, "Root Reduced Matrix:");
//Console.WriteLine("\nRoot.LocalBound = " + rootNode.localBound);
rootNode.Route.Add(Cities[0]); // the route starts at itself
// initialize the priority queue (add the root)
priorityQueue.Enqueue(rootNode, 0);
double costOfBSSF = bssf.costOfRoute();
//Console.WriteLine("BSSF cost:" + costOfBSSF);
bool timesUp = false;
while (!timesUp && priorityQueue.Count > 0)
{
BBNode node = priorityQueue.Dequeue();
if (node.localBound < costOfBSSF)
{
foreach (int child in node.children)
{
// Check if time has expired
if (timer.Elapsed.TotalMilliseconds > time_limit)
{
timesUp = true;
}
// Find the cost to the child node from the current node
int costToNode = node.costMatrix[node.rowIndex, child];
if ((costToNode < int.MaxValue) && (costToNode + node.localBound) < costOfBSSF) // we want to create a new state
{
List<int> childrenToPass = new List<int>(node.children);
childrenToPass.Remove(child);
int[,] childMatrix = infinityOutMatrix(node.costMatrix, node.rowIndex, child);
BBNode childNode = new BBNode(childrenToPass, childMatrix, child); // Create a state
childNode.localBound = node.localBound + node.costMatrix[node.rowIndex, child];
childNode.reduceMatrix();
childNode.Route.AddRange(node.Route);
childNode.Route.Add(Cities[child]);
numStatesCreated++;
// if it's a leaf, update the BSSF
if (childNode.children.Count == 0)
{
if (childNode.localBound < costOfBSSF)
{
bssf = new TSPSolution(childNode.Route);
costOfBSSF = bssf.costOfRoute();
intermediateSolutions++;
}
}
else // otherwise, add it to the queue.
{
priorityQueue.Enqueue(childNode, (float)(childNode.localBound / (childNode.Route.Count * 1000)));
if (priorityQueue.Count > maxInQueue)
{
maxInQueue = priorityQueue.Count;
}
}
}
else
{
numStatesPruned++;
}
// otherwise ignore it. Definitely not part of the solution.
}
}
else numStatesPruned++;
}
timer.Stop();
results[COST] = bssf.costOfRoute().ToString(); // load results into array here, replacing these dummy values
results[TIME] = timer.Elapsed.ToString();
results[COUNT] = intermediateSolutions.ToString();
// Used to fill out the table in the report
String storedStates = "Max Stored States: " + maxInQueue + "\n";
String statesCreated = "Total States Created: " + numStatesCreated + "\n";
String statesPruned = "Total State Pruned: " + numStatesPruned + "\n";
MessageBox.Show(storedStates + statesCreated + statesPruned);
Console.WriteLine(storedStates);
Console.WriteLine(statesCreated);
Console.WriteLine(statesPruned);
return results;
}
// Processes a node in the branch and bound tree
// If it is a leaf node and is better than the current best solution,
// set the bssf to this node. If it is not a leaf, add nodes for each
// unvisited city which is lower than the current upper bound.
private void ProcessBBNode(
IPriorityQueue <BBNode, BBPriority> queue,
Tuple <BBNode, BBPriority> el,
ref int count,
ref double upper,
ref int totalStates,
ref int pruned,
ref int maxQueueSize
)
{
BBNode top = el.Item1;
// Check if the route has passed through every city
if (top.Cities.Count == Cities.Length)
{
// Add the trip back to the starting node.
double cost = top.Cost + top.Matrix.Costs[top.Cities[top.Cities.Count - 1], 0];
if (cost < upper)
{
upper = cost;
count++;
// CLear any nodes with higher cost than the new upper. DEPTH_NONE indicates
// that only cost should be considered, and not depth. Add the pruned nodes
// to the pruned count.
pruned += queue.DeleteElementsHigherThan(new BBPriority(BBPriority.DEPTH_NONE, upper));
ArrayList cities = new ArrayList();
foreach (int city in top.Cities)
{
cities.Add(Cities[city]);
}
bssf = new TSPSolution(cities);
}
}
else
{
// Add nodes to the queue for each potential route out of the current city
int lastCity = top.Cities[top.Cities.Count - 1];
for (int i = 0; i < top.Matrix.Costs.GetLength(0); i++)
{
if (!Double.IsInfinity(top.Matrix.Costs[lastCity, i]))
{
Matrix newMatrix = top.Matrix.FollowRoute(lastCity, i);
double newCost = el.Item2.Cost
+ top.Matrix.Costs[lastCity, i]
+ (newMatrix.LowerBound - top.Matrix.LowerBound);
totalStates++;
// If the prospective state is lower cost than the bssf, add it to the queue
if (newCost < upper)
{
List <int> newCities = top.Cities.Concat(new List <int> {
i
}).ToList();
queue.Insert(
new BBNode(newCities, newMatrix, newCost),
new BBPriority(newCities.Count, newCost)
);
}
else
{
pruned++;
}
}
}
if (queue.Size > maxQueueSize)
{
maxQueueSize = queue.Size;
}
}
}