public void branchAndBound()
{
// start our timer
System.Diagnostics.Stopwatch timer = new System.Diagnostics.Stopwatch();
timer.Start();
int solNumber = 0;
int statesCreated = 0;
int branchesConsidered = 0;
int statesStored = 0;
int statesPruned = 0;
// generate bssf
initBSSF();
double bsf = costOfBssf();
double initial = bsf;
// generate initial cost matrix
state s = new state(Cities.Length);
for (int i = 0; i < Cities.Length; i++)
{
for (int j = 0; j < Cities.Length; j++)
{
if (i == j)
{
s.costMatrix[i, j] = double.PositiveInfinity;
}
else
{
s.costMatrix[i, j] = Cities[i].costToGetTo(Cities[j]);
}
}
}
reduce(s);
// create priority queue and init with initial state
PriorityQueue <state> pq = new PriorityQueue <state>();
pq.Enqueue(s, 0);
// loop - while !empty and cost < bssf{
while (pq.Count > 0)
{
state cur = pq.Dequeue();
if (cur.cost > bsf)
{
statesPruned++;
continue;
}
state nextInc = cur;
state nextEx;
int cityOut = -1;
int cityIn = -1;
double improvement = double.NegativeInfinity;
// for all edges
for (int i = 0; i < cur.numEdges; i++)
{
for (int j = 0; j < cur.numEdges; j++)
{
// if edge is 0
if (cur.costMatrix[i, j] == 0)
{
// calculate best if included
state tmp = includeEdge(cur, i, j);
branchesConsidered++;
// and improvement over exclude
double tmpImprov = worstCase(cur, i, j) - tmp.cost;
// and if keep if best improvement so far
if (improvement < tmpImprov)
{
nextInc = tmp;
cityOut = i;
cityIn = j;
improvement = tmpImprov;
}
}
}
}
if (nextInc.cost < bsf)
{
// is this state a complete solution?
if (nextInc.numAddedEdges == nextInc.numEdges)
{
// transform into bssf
ArrayList route = new ArrayList();
int city = 0;
do
{
route.Add(Cities[city]);
city = nextInc.outEdges[city];
} while (city != 0);
// update
bssf = new TSPSolution(route);
bsf = costOfBssf();
solNumber++;
}
else
{
// we've found the state with the best improvement
// so calculate create the exclude state;
nextEx = new state(cur);
nextEx.costMatrix[cityOut, cityIn] = double.PositiveInfinity;
reduce(nextEx);
// enqueue both of the new states
pq.Enqueue(nextInc, Convert.ToInt32(nextInc.cost / (nextInc.numAddedEdges + 1)));
statesCreated += 2;
// enqueue if not infinite
if (nextEx.cost < bsf)
{
pq.Enqueue(nextEx, Convert.ToInt32(nextEx.cost / (nextInc.numAddedEdges + 1)));
}
else
{
statesPruned++;
}
// die with soemthing if we never actually expanded the state
if (nextInc == cur)
{
throw new NotSupportedException();
}
}
if (pq.Count > statesStored)
{
statesStored = pq.Count;
}
}
} // end while loop
timer.Stop();
Program.MainForm.tbCostOfTour.Text = " " + bssf.costOfRoute();
Program.MainForm.tbElapsedTime.Text = Convert.ToString(timer.Elapsed);
Program.MainForm.tbStateInfo.Text = Convert.ToString(statesCreated) + "-" + Convert.ToString(statesStored) + "-" + Convert.ToString(statesPruned);
Program.MainForm.tbInitialBSF.Text = Convert.ToString(initial);
Program.MainForm.tbSolutionNum.Text = Convert.ToString(solNumber);
// do a refresh.
Program.MainForm.Invalidate();
} // end function