private Tuple <Ind, Ind> SelectTwoParents(Ind[] currentPopulation, double[] fitnesses)
{
var totalProbability = fitnesses.Sum();
var probabilitySelection = Enumerable.Range(0, populationSize).Select(i => fitnesses[i] / totalProbability).ToArray();
var currentProbability = 0.0;
Ind parent1 = new Ind();
Ind parent2 = new Ind();
for (int i = 0; i < currentPopulation.Count(); i++)
{
currentProbability += probabilitySelection[i];
if (currentProbability >= r.NextDouble())
{
parent1 = currentPopulation[i];
}
if (currentProbability >= r.NextDouble())
{
parent2 = currentPopulation[i];
}
}
var parents = new Tuple <Ind, Ind>(parent1, parent2);
return(parents);
}
private double ComputeFitness(Ind individual)
{
var bitsToInt = Convert.ToInt32(individual.bits, 2);
var fitness = -(Math.Pow(bitsToInt, 2)) + (7 * bitsToInt);
return(fitness);
}
//New child is made using singlepoint crossover
private Tuple <Ind, Ind> Crossover(Tuple <Ind, Ind> parents)
{
var crossoverIndex = (digits / 2);
Ind child1 = new Ind();
Ind child2 = new Ind();
child1.bits = parents.Item1.bits.Substring(0, crossoverIndex) + parents.Item2.bits.Substring((crossoverIndex), (digits - crossoverIndex));
child2.bits = parents.Item2.bits.Substring(0, crossoverIndex) + parents.Item1.bits.Substring((crossoverIndex), (digits - crossoverIndex));
var newChildren = new Tuple <Ind, Ind>(child1, child2);
return(newChildren);
}
private Ind Mutation(Ind child, double mutationRate)
{
StringBuilder sbChild = new StringBuilder(child.bits);
for (int i = 0; i < digits; i++)
{
if (r.NextDouble() < mutationRate)
{
sbChild[i] = ('0' == child.bits[i] ? '1' : '0');
}
}
child.bits = sbChild.ToString();
return(child);
}
public Ind Run()
{
Stopwatch sw = new Stopwatch();
sw.Start();
// initialize the first population
var initialPopulation = Enumerable.Range(0, populationSize).Select(i => CreateIndividual()).ToArray();
var currentPopulation = initialPopulation;
for (int generation = 0; generation < numIterations; generation++)
{
// compute fitness of each individual in the population
var fitnesses = Enumerable.Range(0, populationSize).Select(i => ComputeFitness(currentPopulation[i])).ToArray();
var nextPopulation = new Ind[populationSize];
// apply elitism
int startIndex;
if (elitism)
{
startIndex = 1;
var populationWithFitness = currentPopulation.Select((individual, index) => new Tuple <Ind, double>(individual, fitnesses[index]));
var populationSorted = populationWithFitness.OrderByDescending(tuple => tuple.Item2); // item2 is the fitness
var bestIndividual = populationSorted.First();
nextPopulation[0] = bestIndividual.Item1;
}
else
{
startIndex = 0;
}
// initialize the selection function given the current individuals and their fitnesses
var getTwoParents = SelectTwoParents(currentPopulation, fitnesses);
// create the individuals of the next generation
for (int newInd = startIndex; newInd < populationSize; newInd++)
{
// select two parents
var parents = SelectTwoParents(currentPopulation, fitnesses);
// do a crossover between the selected parents to generate two children (with a certain probability, crossover does not happen and the two parents are kept unchanged)
Tuple <Ind, Ind> offspring;
if (r.NextDouble() < crossoverRate)
{
offspring = Crossover(parents);
}
else
{
offspring = parents;
}
// save the two children in the next population (after mutation)
nextPopulation[newInd++] = Mutation(offspring.Item1, mutationRate);
if (newInd < populationSize) //there is still space for the second children inside the population
{
nextPopulation[newInd] = Mutation(offspring.Item2, mutationRate);
}
}
//the new population becomes the current one
currentPopulation = nextPopulation;
}
//recompute the fitnesses on the final population and return the best individual
var finalFitnesses = Enumerable.Range(0, populationSize).Select(i => ComputeFitness(currentPopulation[i])).ToArray();
Console.WriteLine("Run Time: " + sw.Elapsed);
Console.WriteLine("Average fitness of last population: " + finalFitnesses.Average());
Console.WriteLine("Best fitness of last population: " + finalFitnesses.Max());
return(currentPopulation.Select((individual, index) => new Tuple <Ind, double>(individual, finalFitnesses[index])).OrderByDescending(tuple => tuple.Item2).First().Item1);
}
private Ind CreateIndividual()
{
Ind newIndividual = new Ind(digits, r);
return(newIndividual);
}
