/*
* 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.train.rewrite;
import org.encog.Encog;
import org.encog.ml.ea.genome.Genome;
import org.encog.ml.ea.rules.RewriteRule;
import org.encog.ml.prg.EncogProgram;
import org.encog.ml.prg.ProgramNode;
import org.encog.ml.prg.expvalue.ExpressionValue;
/**
* Rewrite any parts of the tree that are constant with a simple constant value.
*/
public class RewriteConstants implements RewriteRule {
/**
* True if the expression was rewritten.
*/
private boolean rewritten;
/**
* {@inheritDoc}
*/
@Override
public boolean rewrite(Genome g) {
EncogProgram program = ((EncogProgram)g);
this.rewritten = false;
ProgramNode rootNode = program.getRootNode();
ProgramNode rewrite = rewriteNode(rootNode);
if (rewrite != null) {
program.setRootNode(rewrite);
}
return this.rewritten;
}
/**
* Attempt to rewrite the specified node.
* @param node The node to attempt to rewrite.
* @return The rewritten node, the original node, if no rewrite occured.
*/
private ProgramNode rewriteNode(ProgramNode node) {
// first try to rewrite the child node
ProgramNode rewrite = tryNodeRewrite(node);
if (rewrite != null) {
return rewrite;
}
// if we could not rewrite the entire node, rewrite as many children as
// we can
for (int i = 0; i < node.getChildNodes().size(); i++) {
ProgramNode childNode = (ProgramNode)node.getChildNodes().get(i);
rewrite = rewriteNode(childNode);
if (rewrite != null) {
node.getChildNodes().remove(i);
node.getChildNodes().add(i, rewrite);
this.rewritten = true;
}
}
// we may have rewritten some children, but the parent was not
// rewritten, so return null.
return null;
}
/**
* Try to rewrite the specified node.
* @param parentNode The node to attempt rewrite.
* @return The rewritten node, or original node, if no rewrite could happen.
*/
private ProgramNode tryNodeRewrite(ProgramNode parentNode) {
ProgramNode result = null;
if (parentNode.isLeaf()) {
return null;
}
if (parentNode.allConstDescendants()) {
ExpressionValue v = parentNode.evaluate();
double ck = v.toFloatValue();
// do not rewrite if it produces a div by 0 or other bad result.
if( Double.isNaN(ck) || Double.isInfinite(ck) ) {
return result;
}
result = parentNode
.getOwner()
.getContext()
.getFunctions()
.factorProgramNode("#const", parentNode.getOwner(),
new ProgramNode[] {});
// is it an integer?
if( Math.abs( ck- ((int)ck))<Encog.DEFAULT_DOUBLE_EQUAL) {
result.getData()[0] = new ExpressionValue((int)ck);
} else {
result.getData()[0] = v;
}
}
return result;
}
}