/*
* 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.pso;
import org.encog.mathutil.VectorAlgebra;
import org.encog.mathutil.randomize.NguyenWidrowRandomizer;
import org.encog.mathutil.randomize.Randomizer;
import org.encog.ml.CalculateScore;
import org.encog.ml.MLMethod;
import org.encog.ml.TrainingImplementationType;
import org.encog.ml.data.MLDataSet;
import org.encog.ml.train.BasicTraining;
import org.encog.neural.networks.BasicNetwork;
import org.encog.neural.networks.structure.NetworkCODEC;
import org.encog.neural.networks.training.TrainingSetScore;
import org.encog.neural.networks.training.propagation.TrainingContinuation;
import org.encog.util.concurrency.EngineConcurrency;
import org.encog.util.concurrency.TaskGroup;
/**
* Iteratively trains a population of neural networks by applying
* particle swarm optimisation (PSO).
*
* Contributed by:
* Geoffroy Noel
* https://github.com/goffer-looney
*
* References:
* James Kennedy and Russell C. Eberhart, Particle swarm optimization,
* Proceedings of the IEEE International Conference on Neural Networks,
* 1995, pp. 1942-1948
*
* @author Geoffroy Noel
*/
public class NeuralPSO extends BasicTraining {
protected boolean m_multiThreaded = true;
protected VectorAlgebra m_va;
protected CalculateScore m_calculateScore;
protected Randomizer m_randomizer;
// Swarm state and memories.
protected BasicNetwork[] m_networks;
protected double[][] m_velocities;
protected double[][] m_bestVectors;
protected double[] m_bestErrors;
protected int m_bestVectorIndex;
// Although this is redundant with m_bestVectors[m_bestVectorIndex],
// m_bestVectors[m_bestVectorIndex] is not thread safe.
private double[] m_bestVector;
BasicNetwork m_bestNetwork = null;
// Typical range is 20 - 40 for many problems.
// More difficult problems may need much higher value.
// Must be low enough to keep the training process
// computationally efficient.
protected int m_populationSize = 30;
// Determines the size of the search space.
// The position components of particle will be bounded to
// [-maxPos, maxPos]
// A well chosen range can improve the performance.
// -1 is a special value that represents boundless search space.
protected double m_maxPosition = -1;
// Maximum change one particle can take during one iteration.
// Imposes a limit on the maximum absolute value of the velocity
// components of a particle.
// Affects the granularity of the search.
// If too high, particle can fly past optimum solution.
// If too low, particle can get stuck in local minima.
// Usually set to a fraction of the dynamic range of the search
// space (10% was shown to be good for high dimensional problems).
// -1 is a special value that represents boundless velocities.
protected double m_maxVelocity = 2;
// c1, cognitive learning rate >= 0
// tendency to return to personal best position
protected double m_c1 = 2.0;
// c2, social learning rate >= 0
// tendency to move towards the swarm best position
protected double m_c2 = 2.0;
// w, inertia weight.
// Controls global (higher value) vs local exploration
// of the search space.
// Analogous to temperature in simulated annealing.
// Must be chosen carefully or gradually decreased over time.
// Value usually between 0 and 1.
protected double m_inertiaWeight = 0.4;
// If true, the position of the previous global best position
// can be updated *before* the other particles have been modified.
private boolean m_pseudoAsynchronousUpdate = false;
/**
* Constructor.
*
* @param network an initialised Encog network.
* The networks in the swarm will be created with
* the same topology as this network.
* @param randomizer any type of Encog network weight initialisation
* object.
* @param calculateScore any type of Encog network scoring/fitness object.
* @param populationSize the swarm size.
*/
public NeuralPSO(final BasicNetwork network,
final Randomizer randomizer, final CalculateScore calculateScore,
final int populationSize) {
super(TrainingImplementationType.Iterative);
// initialisation of the member variables
m_populationSize = populationSize;
m_randomizer = randomizer;
m_calculateScore = calculateScore;
m_bestNetwork = network;
m_networks = new BasicNetwork[m_populationSize];
m_velocities = null;
m_bestVectors = new double[m_populationSize][];
m_bestErrors = new double[m_populationSize];
m_bestVectorIndex = -1;
// get a vector from the network.
m_bestVector = NetworkCODEC.networkToArray(m_bestNetwork);
m_va = new VectorAlgebra();
}
/**
* Construct a PSO using a training set score function, 20 particles and the
* NguyenWidrowRandomizer randomizer.
* @param network The network to train. an initialised Encog network.
* The networks in the swarm will be created with
* the same topology as this network.
* @param trainingSet The training set.
*/
public NeuralPSO(BasicNetwork network, MLDataSet trainingSet)
{
this(network, new NguyenWidrowRandomizer(), new TrainingSetScore(trainingSet), 20);
}
/**
* Initialise the particle positions and velocities,
* personal and global bests.
* Only does this if they have not yet been initialised.
*/
void initPopulation() {
if (m_velocities == null) {
int dimensionality = m_bestVector.length;
m_velocities = new double[m_populationSize][dimensionality];
// run an initialisation iteration
iterationPSO(true);
}
}
/**
* Runs one PSO iteration over the whole population of networks.
*/
@Override
public void iteration() {
initPopulation();
preIteration();
iterationPSO(false);
postIteration();
}
/**
* Internal method for the iteration of the swarm.
*
* @param init true if this is an initialisation iteration.
*/
protected void iterationPSO(boolean init) {
final TaskGroup group = EngineConcurrency.getInstance().createTaskGroup();
for (int i = 0; i < m_populationSize; i++) {
NeuralPSOWorker worker = new NeuralPSOWorker(this, i, init);
if (!init && this.isMultiThreaded()) {
EngineConcurrency.getInstance().processTask(worker, group);
} else {
worker.run();
}
}
if (this.isMultiThreaded()) {
group.waitForComplete();
}
updateGlobalBestPosition();
}
/**
* Update the velocity, position and personal
* best position of a particle
*
* @param particleIndex index of the particle in the swarm
* @param init if true, the position and velocity
* will be initialised.
*/
protected void updateParticle(int particleIndex, boolean init) {
int i = particleIndex;
double[] particlePosition = null;
if (init) {
// Create a new particle with random values.
// Except the first particle which has the same values
// as the network passed to the algorithm.
if (m_networks[i] == null) {
m_networks[i] = (BasicNetwork) m_bestNetwork.clone();
if (i > 0) m_randomizer.randomize(m_networks[i]);
}
particlePosition = getNetworkState(i);
m_bestVectors[i] = particlePosition;
// randomise the velocity
m_va.randomise(m_velocities[i], m_maxVelocity);
} else {
particlePosition = getNetworkState(i);
updateVelocity(i, particlePosition);
// velocity clamping
m_va.clampComponents(m_velocities[i], m_maxVelocity);
// new position (Xt = Xt-1 + Vt)
m_va.add(particlePosition, m_velocities[i]);
// pin the particle against the boundary of the search space.
// (only for the components exceeding maxPosition)
m_va.clampComponents(particlePosition, m_maxPosition);
setNetworkState(i, particlePosition);
}
updatePersonalBestPosition(i, particlePosition);
}
/**
* Update the velocity of a particle
*
* @param particleIndex index of the particle in the swarm
* @param particlePosition the particle current position vector
*/
protected void updateVelocity(int particleIndex, double[] particlePosition) {
int i = particleIndex;
double[] vtmp = new double[particlePosition.length];
// Standard PSO formula
// inertia weight
m_va.mul(m_velocities[i], m_inertiaWeight);
// cognitive term
m_va.copy(vtmp, m_bestVectors[i]);
m_va.sub(vtmp, particlePosition);
m_va.mulRand(vtmp, m_c1);
m_va.add(m_velocities[i], vtmp);
// social term
if (i != m_bestVectorIndex) {
m_va.copy(vtmp, m_pseudoAsynchronousUpdate ? m_bestVectors[m_bestVectorIndex] : m_bestVector);
m_va.sub(vtmp, particlePosition);
m_va.mulRand(vtmp, m_c2);
m_va.add(m_velocities[i], vtmp);
}
}
/**
* Update the personal best position of a particle.
*
* @param particleIndex index of the particle in the swarm
* @param particlePosition the particle current position vector
*/
protected void updatePersonalBestPosition(int particleIndex, double[] particlePosition) {
// set the network weights and biases from the vector
double score = m_calculateScore.calculateScore(m_networks[particleIndex]);
// update the best vectors (g and i)
if ((m_bestErrors[particleIndex] == 0) || isScoreBetter(score, m_bestErrors[particleIndex])) {
m_bestErrors[particleIndex] = score;
m_va.copy(m_bestVectors[particleIndex], particlePosition);
}
}
/**
* Update the swarm's best position
*/
protected void updateGlobalBestPosition() {
boolean bestUpdated = false;
double currentBestError = getError();
for (int i = 0; i < m_populationSize; i++) {
if ((m_bestVectorIndex == -1) || isScoreBetter(m_bestErrors[i], currentBestError)) {
m_bestVectorIndex = i;
bestUpdated = true;
currentBestError = m_bestErrors[i];
}
}
if (bestUpdated) {
m_va.copy(m_bestVector, m_bestVectors[m_bestVectorIndex]);
m_bestNetwork.decodeFromArray(m_bestVector);
setError(m_bestErrors[m_bestVectorIndex]);
}
}
/**
* Compares two scores.
*
* @param score1 a score
* @param score2 a score
* @return true if score1 is better than score2
*/
boolean isScoreBetter(double score1, double score2) {
return ((m_calculateScore.shouldMinimize() && (score1 < score2)) || ((!m_calculateScore.shouldMinimize()) && (score1 > score2)));
}
@Override
public TrainingContinuation pause() {
return null;
}
@Override
public boolean canContinue() {
return false;
}
@Override
public void resume(TrainingContinuation state) {
}
/**
* Returns the state of a network in the swarm
*
* @param particleIndex index of the network in the swarm
* @return an array of weights and biases for the given network
*/
protected double[] getNetworkState(int particleIndex) {
return NetworkCODEC.networkToArray(m_networks[particleIndex]);
}
/**
* Sets the state of the networks in the swarm
*
* @param particleIndex index of the network in the swarm
* @param state an array of weights and biases
*/
protected void setNetworkState(int particleIndex, double[] state) {
NetworkCODEC.arrayToNetwork(state, m_networks[particleIndex]);
}
/**
* Set the swarm size.
*
* @param populationSize the swarm size
*/
public void setPopulationSize(int populationSize) {
m_populationSize = populationSize;
}
/**
* Returns the swarm size.
*
* @return the swarm size.
*/
public int getPopulationSize() {
return m_populationSize;
}
/**
* Sets the maximum velocity.
*
* @param maxVelocity Maximum velocity / Vmax
*/
public void setMaxVelocity(double maxVelocity) {
m_maxVelocity = maxVelocity;
}
/**
* Get the maximum velocity (Vmax)
*
* @return maximum velocity (Vmax)
*/
public double getMaxVelocity() {
return m_maxVelocity;
}
/**
* Set the boundary of the search space (Xmax)
*
* @param maxPosition maximum value for a component (Xmax)
*/
public void setMaxPosition(double maxPosition) {
m_maxPosition = maxPosition;
}
/**
* Get the boundary of the search space (Xmax)
*
* @return the maximum value a component can take (Xmax)
*/
public double getMaxPosition() {
return m_maxPosition;
}
/**
* Sets the cognition coefficient (c1).
*
* @param c1 cognition coefficient (c1)
*/
public void setC1(double c1) {
m_c1 = c1;
}
/**
* Get the cognition coefficient (c1).
*
* @return the cognition coefficient (c1)
*/
public double getC1() {
return m_c1;
}
/**
* Set the social coefficient (c2).
*
* @param c2 the social coefficient (c2)
*/
public void setC2(double c2) {
m_c2 = c2;
}
/**
* Get the social coefficient (c2).
*
* @return the social coefficient (c2)
*/
public double getC2() {
return m_c2;
}
/**
* Set the inertia weight (w)
*
* @param inertiaWeight the inertia weight (w)
*/
public void setInertiaWeight(double inertiaWeight) {
m_inertiaWeight = inertiaWeight;
}
/**
* Get the inertia weight (w)
*
* @return the inertia weight (w)
*/
public double getInertiaWeight() {
return m_inertiaWeight;
}
/**
* Get a description of all the current settings.
*
* @return a String describing all the current setting in a single line.
*/
public String getDescription() {
return String.format("pop = %d, w = %.2f, c1 = %.2f, c2 = %.2f, Xmax = %.2f, Vmax = %.2f",
m_populationSize, m_inertiaWeight, m_c1, m_c2, m_maxPosition, m_maxVelocity);
}
@Override
/**
* Returns the most fit network in the swarm
*
* @return the most fit network in the swarm
*/
public MLMethod getMethod() {
return m_bestNetwork;
}
/**
* Keep a reference to the passed population of networks.
* This population is not copied, it will evolve during training.
*
* @param initialPopulation the initial population of networks.
*/
public void setInitialPopulation(BasicNetwork[] initialPopulation) {
m_networks = initialPopulation;
}
/**
* Get the multi-threaded mode.
*
* @return true if PSO works in multi-threaded mode
*/
public boolean isMultiThreaded() {
return m_multiThreaded;
}
}