public Individual[] reproduce(Individual[] parents, GAParameterSet params) {
if (parents.length != getRequiredNumberOfParents())
throw new IllegalArgumentException(
"Need "
+ getRequiredNumberOfParents()
+ " parents for reproduction (not "
+ parents.length
+ ")");
// Check correct type for parents, get length:
int bitLen = checkParentsTypeAndLength(parents);
// Chance (1 - xover probability) that parents wont be changed:
final RandomGenerator rnd = params.getRandomGenerator();
if (rnd.nextDouble() >= getXOverProbability()) return makeCopyOfParents(parents, params);
// Get parents bitsrings:
BitString p1 = ((BinaryEncodedIndividual) parents[0]).getBitStringRepresentation();
BitString p2 = ((BinaryEncodedIndividual) parents[1]).getBitStringRepresentation();
// x-over:
final int maxAttempts = params.getMaxBadReproductionAttempts();
int attempts = 0;
boolean kidsAreValid = false;
do {
kidsAreValid = false;
int xPoint = rnd.nextInt(1, bitLen);
// offspring bit strings:
BitString c1 = new BitString(bitLen);
BitString c2 = new BitString(bitLen);
// copy before xover-point:
for (int i = 0; i < xPoint; i++) {
c1.set(i, p1.get(i));
c2.set(i, p2.get(i));
}
// copy after xover-point:
for (int i = xPoint; i < bitLen; i++) {
c1.set(i, p2.get(i));
c2.set(i, p1.get(i));
}
// create children and check if children are valid:
ClassifierIndividual[] kids = createKidsFromEncoding(params, c1, c2);
kidsAreValid = kidsSatisfyConstraints(kids, params);
// return valid kids or have another attempts:
if (kidsAreValid) return kids;
else attempts++;
} while (!kidsAreValid && attempts < maxAttempts);
// all attempts failed:
return makeCopyOfParents(parents, params);
}
private ClassifierIndividual[] createKidsFromEncoding(
GAParameterSet params, BitString c1, BitString c2) {
ClassifierIndividual[] kids = new ClassifierIndividual[getRequiredNumberOfParents()];
kids[0] =
(ClassifierIndividual) params.getIndividualsFactory().createSpecificIndividual(c1, params);
kids[1] =
(ClassifierIndividual) params.getIndividualsFactory().createSpecificIndividual(c2, params);
return kids;
}
protected Individual[] makeCopyOfParents(Individual[] parents, GAParameterSet params) {
Individual[] kids = new Individual[parents.length];
for (int i = 0; i < kids.length; i++) {
kids[i] =
params
.getIndividualsFactory()
.createSpecificIndividual(
((BinaryEncodedIndividual) parents[i]).getBitStringRepresentation(), params);
// kids[i] = (BinaryEncodedIndividual) ((BinaryEncodedIndividual) parents[i]).clone();
kids[i].setFitness(parents[i].getFitness());
}
return kids;
}
private boolean kidsSatisfyConstraints(ClassifierIndividual[] kids, GAParameterSet params) {
ClassifierIndividualFactory fact = (ClassifierIndividualFactory) params.getIndividualsFactory();
for (int i = 0; i < kids.length; i++) if (!fact.valid(kids[i])) return false;
return true;
}