/**
* Returns the Euclidean distance in objective space between the specified solution and the
* nearest solution in the population.
*
* @param problem the problem
* @param solution the solution
* @param population the population
* @return the Euclidean distance in objective space between the specified solution and the
* nearest solution in the population
*/
public static double distanceToNearestSolution(
Problem problem, Solution solution, NondominatedPopulation population) {
double minimum = Double.POSITIVE_INFINITY;
for (int i = 0; i < population.size(); i++) {
minimum = Math.min(minimum, euclideanDistance(problem, solution, population.get(i)));
}
return minimum;
}
@Override
public double evaluate(NondominatedPopulation approximationSet) {
int count = 0;
for (Solution solution1 : referenceSet) {
boolean match = false;
for (Solution solution2 : approximationSet) {
if (comparator == null) {
double distance =
MathArrays.distance(solution1.getObjectives(), solution2.getObjectives());
if (distance < Settings.EPS) {
match = true;
break;
}
} else {
comparator.compare(solution1, solution2);
if (comparator.isSameBox()) {
match = true;
break;
}
}
}
if (match) {
count++;
}
}
return count / (double) referenceSet.size();
}
public static void main(String[] args) {
Properties properties = new Properties();
properties.setProperty("populationSize", "10");
Problem problem = new OneMax(100);
Algorithm algorithm =
AlgorithmFactory.getInstance().getAlgorithm("NSGAII", properties, problem);
while (!algorithm.isTerminated()) {
algorithm.step();
NondominatedPopulation population = algorithm.getResult();
if (population.get(0).getObjective(0) == 0) {
// if all bits are 1
System.out.println(
"Found optimal solution after " + algorithm.getNumberOfEvaluations() + " evaluations!");
break;
}
}
}
/**
* Constructs the contribution indicator using the specified reference set and ε-box
* dominance comparator. Solutions residing in the same ε-box are considered to be
* equivalent.If the comparator is {@code null}, exact matching is used.
*
* @param referenceSet the reference set
* @param comparator the ε-box dominance comparator used to determine if solutions in the
* reference set are covered by solutions in the approximation set; or {@code null} if exact
* matching is used
* @throws IllegalArgumentException if the reference set is empty
*/
public Contribution(
NondominatedPopulation referenceSet, EpsilonBoxDominanceComparator comparator) {
super();
this.comparator = comparator;
if (referenceSet.isEmpty()) {
throw new IllegalArgumentException("reference set is empty");
}
if (comparator == null) {
this.referenceSet = referenceSet;
} else {
this.referenceSet = new EpsilonBoxDominanceArchive(comparator, referenceSet);
}
}
