/// <summary>
/// Choose the next node for an ant to visit. This is based on probability.
/// </summary>
/// <param name="currentIndex">The step we are at in the path.</param>
/// <param name="ant">The ant being evaluated.</param>
/// <returns>The node we will move into.</returns>
private int PickNextNode(int currentIndex, DiscreteAnt ant)
{
if (currentIndex == 0 || Random.NextDouble() < PR)
{
int index;
do
{
index = Random.NextInt(0, _graph.Count);
} while (ant.WasVisited(index));
return(index);
}
double[] prob = CalculateProbability(currentIndex, ant);
double r = Random.NextDouble();
double sum = 0;
for (int i = 0; i < _graph.Count; i++)
{
sum += prob[i];
if (sum >= r)
{
return(i);
}
}
// should not happen!
return(-1);
}
/// <summary>
/// Calculate the probability of a given ant moving to any of the next nodes.
/// </summary>
/// <param name="currentIndex">The index into the path.</param>
/// <param name="ant">The ant.</param>
/// <returns>The probability of moving to the next node.</returns>
private double[] CalculateProbability(int currentIndex, DiscreteAnt ant)
{
double[] result = new double[_graph.Count];
int i = ant.Path[currentIndex - 1];
double d = 0.0;
for (int l = 0; l < _graph.Count; l++)
{
if (!ant.WasVisited(l))
{
d += Math.Pow(_pheromone[i][l], Alpha)
* Math.Pow(1.0 / _graph.Cost(i, l), Beta);
}
}
for (int j = 0; j < _graph.Count; j++)
{
if (ant.WasVisited(j))
{
result[j] = 0.0;
}
else
{
double n = Math.Pow(_pheromone[i][j], Alpha)
* Math.Pow(1.0 / _graph.Cost(i, j), Beta);
result[j] = n / d;
}
}
return(result);
}
/// <summary>
/// Choose the next node for an ant to visit. This is based on probability.
/// </summary>
/// <param name="currentIndex">The step we are at in the path.</param>
/// <param name="ant">The ant being evaluated.</param>
/// <returns>The node we will move into.</returns>
private int PickNextNode(int currentIndex, DiscreteAnt ant)
{
if (currentIndex == 0 || Random.NextDouble() < PR)
{
int index;
do
{
index = Random.NextInt(0, _graph.Count);
} while (ant.WasVisited(index));
return index;
}
double[] prob = CalculateProbability(currentIndex, ant);
double r = Random.NextDouble();
double sum = 0;
for (int i = 0; i < _graph.Count; i++)
{
sum += prob[i];
if (sum >= r)
return i;
}
// should not happen!
return -1;
}
/// <summary>
/// Calculate the probability of a given ant moving to any of the next nodes.
/// </summary>
/// <param name="currentIndex">The index into the path.</param>
/// <param name="ant">The ant.</param>
/// <returns>The probability of moving to the next node.</returns>
private double[] CalculateProbability(int currentIndex, DiscreteAnt ant)
{
double[] result = new double[_graph.Count];
int i = ant.Path[currentIndex - 1];
double d = 0.0;
for (int l = 0; l < _graph.Count; l++)
if (!ant.WasVisited(l))
d += Math.Pow(_pheromone[i][l], Alpha)
* Math.Pow(1.0 / _graph.Cost(i, l), Beta);
for (int j = 0; j < _graph.Count; j++)
{
if (ant.WasVisited(j))
{
result[j] = 0.0;
}
else
{
double n = Math.Pow(_pheromone[i][j], Alpha)
* Math.Pow(1.0 / _graph.Cost(i, j), Beta);
result[j] = n / d;
}
}
return result;
}
