private double computeFitness(Ind individual)
{
// -(Pow(x)) + 7x
var fitness = -(Math.Pow(individual.value(), 2)) + (7 * individual.value());
return(fitness);
}
// Create 2 childs from the parents
private Tuple <Ind, Ind> crossover(Tuple <Ind, Ind> parents)
{
int cutoff = parents.Item1.binary.Length / 2;
Ind child1 = new Ind();
Ind child2 = new Ind();
child1.binary = parents.Item1.binary.Substring(0, cutoff) + parents.Item2.binary.Substring(cutoff);
child2.binary = parents.Item2.binary.Substring(0, cutoff) + parents.Item1.binary.Substring(cutoff);
return(new Tuple <Ind, Ind>(child1, child2));
}
/* Roulette selection */
private Func <Tuple <Ind, Ind> > selectTwoParents(Ind[] population, double[] fitnesses)
{
// Normalize the values
var lowestFitness = fitnesses.OrderBy(x => x).First();
var highestFitness = fitnesses.OrderBy(x => x).Last();
double[] normalizedFitnesses = new double[fitnesses.Length];
// All values are between 0-1
for (var i = 0; i < fitnesses.Length; i++)
{
normalizedFitnesses[i] = (fitnesses[i] - lowestFitness) / (highestFitness - lowestFitness);
}
var cumProbability = 0.0;
var totalProbability = normalizedFitnesses.Sum();
var avgNormalizedFitnesses = Enumerable.Range(0, populationSize).Select(i => normalizedFitnesses[i] / totalProbability).ToArray();
Ind parent1 = new Ind();
Ind parent2 = new Ind();
for (int i = 0; i < populationSize; i++)
{
cumProbability += normalizedFitnesses[i];
if (cumProbability >= r.NextDouble())
{
if (parent1.value() == 0)
{
parent1 = population[i];
}
else
{
parent2 = population[i];
break;
}
}
}
return(() => { return new Tuple <Ind, Ind>(parent1, parent2); });
}
private Ind mutation(Ind individual, double mutationRate)
{
StringBuilder mutation = new StringBuilder(individual.binary);
for (int i = 0; i < 5; i++)
{
if (r.NextDouble() < mutationRate)
{
if (individual.binary[i] == '0')
{
mutation[i] = '1';
}
else
{
mutation[i] = '0';
}
}
}
individual.binary = mutation.ToString();
return(individual);
}
public Ind Run()
{
// 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 = getTwoParents();
// 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;
// in case it's needed, check here some convergence condition to terminate the generations loop earlier
}
// 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("// After running the Genetic Algorithm \\");
Console.WriteLine("Average Fitness of last population " + finalFitnesses.Average());
Console.WriteLine("Best Fitness of last population " + finalFitnesses.OrderBy(x => x).Last());
return(currentPopulation.Select((individual, index) => new Tuple <Ind, double>(individual, finalFitnesses[index])).OrderByDescending(tuple => tuple.Item2).First().Item1);
}
