// Evolves a population over one generation
public static Population evolvePopulation(Population pop)
{
Population newPopulation = new Population(pop.populationSize(), false);
// Keep our best individual if elitism is enabled
int elitismOffset = 0;
if (elitism)
{
newPopulation.saveSac(0, pop.getFittest());
elitismOffset = 1;
}
// Crossover population
// Loop over the new population's size and create individuals from
// Current population
for (int i = elitismOffset; i < newPopulation.populationSize(); i++)
{
// Select parents
Knapsack parent1 = tournamentSelection(pop);
Knapsack parent2 = tournamentSelection(pop);
// Crossover parents
Knapsack child = crossover(parent1, parent2);
// Add child to new population
newPopulation.saveSac(i, child);
}
// Mutate the new population a bit to add some new genetic material
for (int i = elitismOffset; i < newPopulation.populationSize(); i++)
{
mutate(newPopulation.getSac(i));
}
return(newPopulation);
}
// Mutate a tour using swap mutation
private static void mutate(Knapsack sac)
{
Random rnd = new Random();
// Loop through tour cities
for (int i = 0; i < sac.getObjects().Length; i++)
{
// Apply mutation rate
if (rnd.NextDouble() < mutationRate)
{
// Get a second random position in the tour
int mutationPos = (int)(sac.getObjects().Length *rnd.NextDouble());
if (sac.getObjects()[mutationPos])
{
sac.setoneObject(i, false);
sac.processValue();
sac.processWeight();
}
else
{
if (sac.getWeight() + MainForm.listItems[i].Weight <= sac.getCapacity())
{
sac.setoneObject(i, true);
sac.processValue();
sac.processWeight();
}
}
}
}
}
// Gets the best tour in the population
public Knapsack getFittest()
{
Knapsack fittest = sacs[0];
for (int i = 1; i < populationSize(); i++)
{
if (fittest.getFitness() <= getSac(i).getFitness())
{
fittest = getSac(i);
}
}
return(fittest);
}
// Construct a population
public Population(int populationSize, bool initialise)
{
sacs = new Knapsack[populationSize];
if (initialise)
{
// Loop and create individuals
for (int i = 0; i < populationSize; i++)
{
Knapsack newSacs = new Knapsack();
newSacs.generateIndividual();
saveSac(i, newSacs);
}
}
}
// Selects candidate tour for crossover
private static Knapsack tournamentSelection(Population pop)
{
Random rnd = new Random();
// Create a tournament population
Population tournament = new Population(tournamentSize, false);
// For each place in the tournament get a random candidate tour and
// add it
for (int i = 0; i < tournamentSize; i++)
{
int randomId = (int)(rnd.NextDouble() * pop.populationSize());
tournament.saveSac(i, pop.getSac(randomId));
}
// Get the fittest tour
Knapsack fittest = tournament.getFittest();
return(fittest);
}
// Applies crossover to a set of parents and creates offspring
public static Knapsack crossover(Knapsack parent1, Knapsack parent2)
{
Random rnd = new Random();
// Create new child tour
Knapsack child = new Knapsack();
// Get start and end sub tour positions for parent1's tour
int crossPos = (int)(rnd.NextDouble() * parent1.getObjects().Length);
// Loop and add the sub tour from parent1 to our child
for (int i = 0; i < child.getObjects().Length; i++)
{
if (i < crossPos)
{
child.processWeight();
if (child.getWeight() + MainForm.listItems[i].Weight <= child.getCapacity())
{
child.setoneObject(i, parent2.getoneObject(i));
child.processWeight();
}
}
else
{
child.processWeight();
if (child.getWeight() + MainForm.listItems[i].Weight <= child.getCapacity())
{
child.setoneObject(i, parent1.getoneObject(i));
child.processWeight();
}
}
}
child.processValue();
return(child);
}
// Saves a tour
public void saveSac(int index, Knapsack sac)
{
sacs[index] = sac;
}