/*
* Encog(tm) Core v3.4 - Java Version
* http://www.heatonresearch.com/encog/
* https://github.com/encog/encog-java-core
* Copyright 2008-2016 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.neural.networks.training.propagation.back;
import org.encog.ml.data.MLDataSet;
import org.encog.neural.networks.ContainsFlat;
import org.encog.neural.networks.training.LearningRate;
import org.encog.neural.networks.training.Momentum;
import org.encog.neural.networks.training.TrainingError;
import org.encog.neural.networks.training.propagation.Propagation;
import org.encog.neural.networks.training.propagation.TrainingContinuation;
import org.encog.neural.networks.training.strategy.SmartLearningRate;
import org.encog.neural.networks.training.strategy.SmartMomentum;
import org.encog.util.validate.ValidateNetwork;
/**
* This class implements a backpropagation training algorithm for feed forward
* neural networks. It is used in the same manner as any other training class
* that implements the Train interface.
*
* Backpropagation is a common neural network training algorithm. It works by
* analyzing the error of the output of the neural network. Each neuron in the
* output layer's contribution, according to weight, to this error is
* determined. These weights are then adjusted to minimize this error. This
* process continues working its way backwards through the layers of the neural
* network.
*
* This implementation of the backpropagation algorithm uses both momentum and a
* learning rate. The learning rate specifies the degree to which the weight
* matrixes will be modified through each iteration. The momentum specifies how
* much the previous learning iteration affects the current. To use no momentum
* at all specify zero.
*
* One primary problem with backpropagation is that the magnitude of the partial
* derivative is often detrimental to the training of the neural network. The
* other propagation methods of Manhatten and Resilient address this issue in
* different ways. In general, it is suggested that you use the resilient
* propagation technique for most Encog training tasks over back propagation.
*/
public class Backpropagation extends Propagation implements Momentum,
LearningRate {
/**
* The resume key for backpropagation.
*/
public static final String LAST_DELTA = "LAST_DELTA";
/**
* The learning rate.
*/
private double learningRate;
/**
* The momentum.
*/
private double momentum;
/**
* The last delta values.
*/
private double[] lastDelta;
/**
* Should Nesterov momentum be used?
*/
private boolean nesterovUpdate;
/**
* Create a class to train using backpropagation. Use auto learn rate and
* momentum. Use the CPU to train.
*
* @param network
* The network that is to be trained.
* @param training
* The training data to be used for backpropagation.
*/
public Backpropagation(final ContainsFlat network, final MLDataSet training) {
this(network, training, 0, 0);
addStrategy(new SmartLearningRate());
addStrategy(new SmartMomentum());
}
/**
*
* @param network
* The network that is to be trained
* @param training
* The training set
* @param theLearnRate
* The rate at which the weight matrix will be adjusted based on
* learning.
* @param theMomentum
* The influence that previous iteration's training deltas will
* have on the current iteration.
*/
public Backpropagation(final ContainsFlat network,
final MLDataSet training, final double theLearnRate,
final double theMomentum) {
super(network, training);
ValidateNetwork.validateMethodToData(network, training);
this.momentum = theMomentum;
this.learningRate = theLearnRate;
this.lastDelta = new double[network.getFlat().getWeights().length];
}
/**
* {@inheritDoc}
*/
@Override
public boolean canContinue() {
return false;
}
/**
* @return The last delta values.
*/
public double[] getLastDelta() {
return this.lastDelta;
}
/**
* @return The learning rate, this is value is essentially a percent. It is
* the degree to which the gradients are applied to the weight
* matrix to allow learning.
*/
@Override
public double getLearningRate() {
return this.learningRate;
}
/**
* @return The momentum for training. This is the degree to which changes
* from which the previous training iteration will affect this
* training iteration. This can be useful to overcome local minima.
*/
@Override
public double getMomentum() {
return this.momentum;
}
/**
* Determine if the specified continuation object is valid to resume with.
*
* @param state
* The continuation object to check.
* @return True if the specified continuation object is valid for this
* training method and network.
*/
public boolean isValidResume(final TrainingContinuation state) {
if (!state.getContents().containsKey(Backpropagation.LAST_DELTA)) {
return false;
}
if (!state.getTrainingType().equals(getClass().getSimpleName())) {
return false;
}
final double[] d = (double[]) state.get(Backpropagation.LAST_DELTA);
return d.length == ((ContainsFlat) getMethod()).getFlat().getWeights().length;
}
/**
* Pause the training.
*
* @return A training continuation object to continue with.
*/
@Override
public TrainingContinuation pause() {
final TrainingContinuation result = new TrainingContinuation();
result.setTrainingType(this.getClass().getSimpleName());
result.set(Backpropagation.LAST_DELTA, this.lastDelta);
return result;
}
/**
* Resume training.
*
* @param state
* The training state to return to.
*/
@Override
public void resume(final TrainingContinuation state) {
if (!isValidResume(state)) {
throw new TrainingError("Invalid training resume data length");
}
this.lastDelta = ((double[]) state.get(Backpropagation.LAST_DELTA));
}
/**
* Set the learning rate, this is value is essentially a percent. It is the
* degree to which the gradients are applied to the weight matrix to allow
* learning.
*
* @param rate
* The learning rate.
*/
@Override
public void setLearningRate(final double rate) {
this.learningRate = rate;
}
/**
* Set the momentum for training. This is the degree to which changes from
* which the previous training iteration will affect this training
* iteration. This can be useful to overcome local minima.
*
* @param m
* The momentum.
*/
@Override
public void setMomentum(final double m) {
this.momentum = m;
}
/**
* Update a weight.
*
* @param gradients
* The gradients.
* @param lastGradient
* The last gradients.
* @param index
* The index.
* @return The weight delta.
*/
@Override
public double updateWeight(final double[] gradients,
final double[] lastGradient, final int index) {
final double delta = (gradients[index] * this.learningRate)
+ (this.lastDelta[index] * this.momentum);
this.lastDelta[index] = delta;
return delta;
}
/**
* Update a weight.
*
* @param gradients
* The gradients.
* @param lastGradient
* The last gradients.
* @param index
* The index.
* @param dropoutRate
* The dropout rate.
* @return The weight delta.
*/
@Override
public double updateWeight(final double[] gradients,
final double[] lastGradient, final int index, double dropoutRate) {
if(this.nesterovUpdate) {
return updateWeightNesterov(gradients,lastGradient,index,dropoutRate);
} else {
return updateWeightNormal(gradients,lastGradient,index,dropoutRate);
}
}
/**
* Update a weight.
*
* @param gradients
* The gradients.
* @param lastGradient
* The last gradients.
* @param index
* The index.
* @param dropoutRate
* The dropout rate.
* @return The weight delta.
*/
private double updateWeightNormal(final double[] gradients,
final double[] lastGradient, final int index, double dropoutRate) {
if (dropoutRate > 0 && dropoutRandomSource.nextDouble() < dropoutRate) {
return 0;
};
final double delta = (gradients[index] * this.learningRate)
+ (this.lastDelta[index] * this.momentum);
this.lastDelta[index] = delta;
return delta;
}
/**
* Update a weight (Nesterov).
*
* @param gradients
* The gradients.
* @param lastGradient
* The last gradients.
* @param index
* The index.
* @param dropoutRate
* The dropout rate.
* @return The weight delta.
*/
private double updateWeightNesterov(final double[] gradients,
final double[] lastGradient, final int index, double dropoutRate) {
if (dropoutRate > 0 && dropoutRandomSource.nextDouble() < dropoutRate) {
return 0;
};
double prevNesterov = this.lastDelta[index];
this.lastDelta[index] = (this.momentum * prevNesterov)
+ (this.gradients[index] * this.learningRate);
final double delta = (this.momentum * prevNesterov) - ((1+this.momentum)*this.lastDelta[index]);
this.lastDelta[index] = delta;
return delta;
}
/**
* Perform training method specific init.
*/
public void initOthers() {
}
public boolean isNesterovUpdate() {
return nesterovUpdate;
}
public void setNesterovUpdate(boolean nesterovUpdate) {
this.nesterovUpdate = nesterovUpdate;
}
}
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