public static Ant RunMMAS(Graph graph, Parameters parameters, UInt32 iterations)
{
var greedySolution = CreateSolutionNN(graph);
var greedyCost = graph.CalculateRouteLength(greedySolution.visited);
var initialLimits = CalcTrailLimitsMMAS(parameters, graph.dimension, greedyCost);
var minPheromone = initialLimits.Item1;
var maxPheromone = initialLimits.Item2;
PheromoneMemory pheromone = new PheromoneMemory(graph.dimension, maxPheromone);
double[] heuristic = new double[graph.dimension * graph.dimension];
foreach (var distance in graph.edgeWeight)
{
for (int i = 0; i < graph.dimension; i++)
{
for (int j = 0; j < graph.dimension; j++)
{
heuristic[j + (graph.dimension * i)] = (1 / Math.Pow(graph.edgeWeight[i, j], parameters.beta));
}
}
}
Ant[] ants = new Ant[parameters.antsCount];
for (int i = 0; i < parameters.antsCount; i++)
{
ants[i] = new Ant();
}
Ant bestAnt = new Ant();
for (UInt32 iteration = 0; iteration < iterations; ++iteration)
{
foreach (Ant ant in ants)
{
ant.Initialize(graph.dimension);
var startNode = GetRandomUInt32(0, graph.dimension - 1);
ant.Visit(startNode);
for (UInt32 j = 1; j < graph.dimension; ++j)
{
moveAntMMAS(graph, pheromone, heuristic, ant);
}
ant.cost = graph.CalculateRouteLength(ant.visited);
}
var iterationBest = ants[0];
bool newBestFound = false;
foreach (Ant ant in ants)
{
if (ant.cost < bestAnt.cost)
{
bestAnt = ant;
newBestFound = true;
Console.WriteLine("New best solution found with the cost: {0} at iteration {1}", bestAnt.cost, iteration);
}
if (ant.cost < iterationBest.cost)
{
iterationBest = ant;
}
}
if (newBestFound)
{
var limits = CalcTrailLimitsMMAS(parameters, graph.dimension, bestAnt.cost);
minPheromone = limits.Item1;
maxPheromone = limits.Item2;
}
pheromone.EvaporateFromAll(parameters.GetEvaporationRate(), minPheromone);
var updateAnt = iterationBest;
double deposite = 1.0 / updateAnt.cost;
var previousNode = updateAnt.visited[updateAnt.visited.Count - 1];
foreach (var node in updateAnt.visited)
{
pheromone.Increase(previousNode, node, deposite, maxPheromone, graph.isSymetric);
previousNode = node;
}
}
return(bestAnt);
}
public static UInt32 moveAntMMAS(Graph graph, PheromoneMemory pheromone, double [] heuristic, Ant ant)
{
var dimension = graph.dimension;
var currentNode = ant.visited[ant.visited.Count - 1];
UInt32 offset = currentNode * dimension;
UInt32 [] candList = new UInt32 [MaxCandListSize];
UInt32 candListSize = 0;
for (int i = 0; i < graph.dimension; i++)
{
if (!ant.IsVisited((UInt32)i))
{
candList[candListSize] = (UInt32)i;
++candListSize;
}
}
UInt32 chosenNode = currentNode;
if (candListSize > 0)
{
double[] productsPrefixSum = new double[MaxCandListSize];
double total = 0;
for (UInt32 j = 0; j < candListSize; ++j)
{
var node = candList[j];
var product = pheromone.Get(currentNode, node) * heuristic[offset + node];
total += product;
productsPrefixSum[j] = total;
}
chosenNode = candList[candListSize - 1];
var r = GetRandomDouble() * total;
for (UInt32 i = 0; i < candListSize; ++i)
{
if (r < productsPrefixSum[i])
{
chosenNode = candList[i];
break;
}
}
}
else
{
double maxProduct = 0;
for (UInt32 node = 0; node < dimension; ++node)
{
if (!ant.IsVisited(node))
{
var product = pheromone.Get(currentNode, node) * heuristic[offset + node];
if (product > maxProduct)
{
maxProduct = product;
chosenNode = node;
}
}
}
}
ant.Visit(chosenNode);
return(chosenNode);
}
