/*
* Encog(tm) Core v3.3 - Java Version
* http://www.heatonresearch.com/encog/
* https://github.com/encog/encog-java-core
* Copyright 2008-2014 Heaton Research, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* For more information on Heaton Research copyrights, licenses
* and trademarks visit:
* http://www.heatonresearch.com/copyright
*/
package org.encog.ml.prg.opp;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import org.encog.ml.ea.genome.Genome;
import org.encog.ml.ea.opp.EvolutionaryOperator;
import org.encog.ml.ea.train.EvolutionaryAlgorithm;
import org.encog.ml.prg.EncogProgram;
import org.encog.ml.prg.EncogProgramContext;
import org.encog.ml.prg.ProgramNode;
import org.encog.ml.prg.expvalue.ValueType;
import org.encog.ml.prg.generator.PrgGenerator;
import org.encog.ml.prg.generator.PrgGrowGenerator;
/**
* Perform a type-safe subtree mutation. The mutation point is chosen randomly,
* but the new tree will be generated with compatible types to the parent.
*/
public class SubtreeMutation implements EvolutionaryOperator {
/**
* A random generator.
*/
private PrgGenerator generator;
/**
* The maximum depth.
*/
private final int maxDepth;
/**
* Construct the subtree mutation object.
* @param theContext The program context.
* @param theMaxDepth The maximum depth.
*/
public SubtreeMutation(final EncogProgramContext theContext,
final int theMaxDepth) {
this.generator = new PrgGrowGenerator(theContext, theMaxDepth);
this.maxDepth = theMaxDepth;
}
/**
* This method is called reflexivly as we iterate downward. Once we reach
* the desired point (when current level drops to zero), the operation is
* performed.
*
* @param rnd
* A random number generator.
* @param parentNode
* The parent node.
* @param types
* The desired node
* @param holder
* The level holder.
*/
private void findNode(final Random rnd, final EncogProgram result,
final ProgramNode parentNode, final List<ValueType> types,
final int[] globalIndex) {
if (globalIndex[0] == 0) {
globalIndex[0]--;
final ProgramNode newInsert = this.generator.createNode(rnd,
result, this.maxDepth, types);
result.replaceNode(parentNode, newInsert);
} else {
globalIndex[0]--;
for (int i = 0; i < parentNode.getTemplate().getChildNodeCount(); i++) {
final ProgramNode childNode = parentNode.getChildNode(i);
final List<ValueType> childTypes = parentNode.getTemplate()
.getParams().get(i).determineArgumentTypes(types);
findNode(rnd, result, childNode, childTypes, globalIndex);
}
}
}
/**
* @return The random tree generator to use.
*/
public PrgGenerator getGenerator() {
return this.generator;
}
/**
* {@inheritDoc}
*/
@Override
public void init(final EvolutionaryAlgorithm theOwner) {
// TODO Auto-generated method stub
}
/**
* @return Returns the number of offspring produced. In this case, one.
*/
@Override
public int offspringProduced() {
return 1;
}
/**
* @return Returns the number of parents needed. In this case, one.
*/
@Override
public int parentsNeeded() {
return 1;
}
/**
* {@inheritDoc}
*/
@Override
public void performOperation(final Random rnd, final Genome[] parents,
final int parentIndex, final Genome[] offspring,
final int offspringIndex) {
final EncogProgram program = (EncogProgram) parents[0];
final EncogProgramContext context = program.getContext();
final EncogProgram result = context.cloneProgram(program);
final List<ValueType> types = new ArrayList<ValueType>();
types.add(context.getResult().getVariableType());
final int[] globalIndex = new int[1];
globalIndex[0] = rnd.nextInt(result.getRootNode().size());
findNode(rnd, result, result.getRootNode(), types, globalIndex);
offspring[0] = result;
}
/**
* Set the random tree generator to use.
* @param generator The random tree generator.
*/
public void setGenerator(final PrgGenerator generator) {
this.generator = generator;
}
}