diff --git a/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Constants.java b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Constants.java new file mode 100644 index 0000000000..b646c686b2 --- /dev/null +++ b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Constants.java @@ -0,0 +1,47 @@ +package com.baeldung.algorithms.multiswarm; + +/** + * Constants used by the Multi-swarm optimization algorithms. + * + * @author Donato Rimenti + * + */ +public class Constants { + + /** + * The inertia factor encourages a particle to continue moving in its + * current direction. + */ + public static final double INERTIA_FACTOR = 0.729; + + /** + * The cognitive weight encourages a particle to move toward its historical + * best-known position. + */ + public static final double COGNITIVE_WEIGHT = 1.49445; + + /** + * The social weight encourages a particle to move toward the best-known + * position found by any of the particle’s swarm-mates. + */ + public static final double SOCIAL_WEIGHT = 1.49445; + + /** + * The global weight encourages a particle to move toward the best-known + * position found by any particle in any swarm. + */ + public static final double GLOBAL_WEIGHT = 0.3645; + + /** + * Upper bound for the random generation. We use it to reduce the + * computation time since we can rawly estimate it. + */ + public static final int PARTICLE_UPPER_BOUND = 10000000; + + /** + * Private constructor for utility class. + */ + private Constants() { + } + +} diff --git a/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/FitnessFunction.java b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/FitnessFunction.java new file mode 100644 index 0000000000..2d86ec8d94 --- /dev/null +++ b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/FitnessFunction.java @@ -0,0 +1,21 @@ +package com.baeldung.algorithms.multiswarm; + +/** + * Interface for a fitness function, used to decouple the main algorithm logic + * from the specific problem solution. + * + * @author Donato Rimenti + * + */ +public interface FitnessFunction { + + /** + * Returns the fitness of a particle given its position. + * + * @param particlePosition + * the position of the particle + * @return the fitness of the particle + */ + public double getFitness(long[] particlePosition); + +} diff --git a/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Multiswarm.java b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Multiswarm.java new file mode 100644 index 0000000000..ef60726278 --- /dev/null +++ b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Multiswarm.java @@ -0,0 +1,227 @@ +package com.baeldung.algorithms.multiswarm; + +import java.util.Arrays; +import java.util.Random; + +/** + * Represents a collection of {@link Swarm}. + * + * @author Donato Rimenti + * + */ +public class Multiswarm { + + /** + * The swarms managed by this multiswarm. + */ + private Swarm[] swarms; + + /** + * The best position found within all the {@link #swarms}. + */ + private long[] bestPosition; + + /** + * The best fitness score found within all the {@link #swarms}. + */ + private double bestFitness = Double.NEGATIVE_INFINITY; + + /** + * A random generator. + */ + private Random random = new Random(); + + /** + * The fitness function used to determine how good is a particle. + */ + private FitnessFunction fitnessFunction; + + /** + * Instantiates a new Multiswarm. + * + * @param numSwarms + * the number of {@link #swarms} + * @param particlesPerSwarm + * the number of particle for each {@link #swarms} + * @param fitnessFunction + * the {@link #fitnessFunction} + */ + public Multiswarm(int numSwarms, int particlesPerSwarm, FitnessFunction fitnessFunction) { + this.fitnessFunction = fitnessFunction; + this.swarms = new Swarm[numSwarms]; + for (int i = 0; i < numSwarms; i++) { + swarms[i] = new Swarm(particlesPerSwarm); + } + } + + /** + * Main loop of the algorithm. Iterates all particles of all + * {@link #swarms}. For each particle, computes the new fitness and checks + * if a new best position has been found among itself, the swarm and all the + * swarms and finally updates the particle position and speed. + */ + public void mainLoop() { + for (Swarm swarm : swarms) { + for (Particle particle : swarm.getParticles()) { + + long[] particleOldPosition = particle.getPosition().clone(); + + // Calculate the particle fitness. + particle.setFitness(fitnessFunction.getFitness(particleOldPosition)); + + // Check if a new best position has been found for the particle + // itself, within the swarm and the multiswarm. + if (particle.getFitness() > particle.getBestFitness()) { + particle.setBestFitness(particle.getFitness()); + particle.setBestPosition(particleOldPosition); + + if (particle.getFitness() > swarm.getBestFitness()) { + swarm.setBestFitness(particle.getFitness()); + swarm.setBestPosition(particleOldPosition); + + if (swarm.getBestFitness() > bestFitness) { + bestFitness = swarm.getBestFitness(); + bestPosition = swarm.getBestPosition().clone(); + } + + } + } + + // Updates the particle position by adding the speed to the + // actual position. + long[] position = particle.getPosition(); + long[] speed = particle.getSpeed(); + + position[0] += speed[0]; + position[1] += speed[1]; + + // Updates the particle speed. + speed[0] = getNewParticleSpeedForIndex(particle, swarm, 0); + speed[1] = getNewParticleSpeedForIndex(particle, swarm, 1); + } + } + } + + /** + * Computes a new speed for a given particle of a given swarm on a given + * axis. The new speed is computed using the formula: + * + *
+ * ({@link Constants#INERTIA_FACTOR} * {@link Particle#getSpeed()}) +
+ * (({@link Constants#COGNITIVE_WEIGHT} * random(0,1)) * ({@link Particle#getBestPosition()} - {@link Particle#getPosition()})) +
+ * (({@link Constants#SOCIAL_WEIGHT} * random(0,1)) * ({@link Swarm#getBestPosition()} - {@link Particle#getPosition()})) +
+ * (({@link Constants#GLOBAL_WEIGHT} * random(0,1)) * ({@link #bestPosition} - {@link Particle#getPosition()}))
+ *
+ *
+ * @param particle
+ * the particle whose new speed needs to be computed
+ * @param swarm
+ * the swarm which contains the particle
+ * @param index
+ * the index of the particle axis whose speeds needs to be
+ * computed
+ * @return the new speed of the particle passed on the given axis
+ */
+ private int getNewParticleSpeedForIndex(Particle particle, Swarm swarm, int index) {
+ return (int) ((Constants.INERTIA_FACTOR * particle.getSpeed()[index])
+ + (randomizePercentage(Constants.COGNITIVE_WEIGHT)
+ * (particle.getBestPosition()[index] - particle.getPosition()[index]))
+ + (randomizePercentage(Constants.SOCIAL_WEIGHT)
+ * (swarm.getBestPosition()[index] - particle.getPosition()[index]))
+ + (randomizePercentage(Constants.GLOBAL_WEIGHT)
+ * (bestPosition[index] - particle.getPosition()[index])));
+ }
+
+ /**
+ * Returns a random number between 0 and the value passed as argument.
+ *
+ * @param value
+ * the value to randomize
+ * @return a random value between 0 and the one passed as argument
+ */
+ private double randomizePercentage(double value) {
+ return random.nextDouble() * value;
+ }
+
+ /**
+ * Gets the {@link #bestPosition}.
+ *
+ * @return the {@link #bestPosition}
+ */
+ public long[] getBestPosition() {
+ return bestPosition;
+ }
+
+ /**
+ * Gets the {@link #bestFitness}.
+ *
+ * @return the {@link #bestFitness}
+ */
+ public double getBestFitness() {
+ return bestFitness;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#hashCode()
+ */
+ @Override
+ public int hashCode() {
+ final int prime = 31;
+ int result = 1;
+ long temp;
+ temp = Double.doubleToLongBits(bestFitness);
+ result = prime * result + (int) (temp ^ (temp >>> 32));
+ result = prime * result + Arrays.hashCode(bestPosition);
+ result = prime * result + ((fitnessFunction == null) ? 0 : fitnessFunction.hashCode());
+ result = prime * result + ((random == null) ? 0 : random.hashCode());
+ result = prime * result + Arrays.hashCode(swarms);
+ return result;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#equals(java.lang.Object)
+ */
+ @Override
+ public boolean equals(Object obj) {
+ if (this == obj)
+ return true;
+ if (obj == null)
+ return false;
+ if (getClass() != obj.getClass())
+ return false;
+ Multiswarm other = (Multiswarm) obj;
+ if (Double.doubleToLongBits(bestFitness) != Double.doubleToLongBits(other.bestFitness))
+ return false;
+ if (!Arrays.equals(bestPosition, other.bestPosition))
+ return false;
+ if (fitnessFunction == null) {
+ if (other.fitnessFunction != null)
+ return false;
+ } else if (!fitnessFunction.equals(other.fitnessFunction))
+ return false;
+ if (random == null) {
+ if (other.random != null)
+ return false;
+ } else if (!random.equals(other.random))
+ return false;
+ if (!Arrays.equals(swarms, other.swarms))
+ return false;
+ return true;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#toString()
+ */
+ @Override
+ public String toString() {
+ return "Multiswarm [swarms=" + Arrays.toString(swarms) + ", bestPosition=" + Arrays.toString(bestPosition)
+ + ", bestFitness=" + bestFitness + ", random=" + random + ", fitnessFunction=" + fitnessFunction + "]";
+ }
+
+}
diff --git a/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Particle.java b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Particle.java
new file mode 100644
index 0000000000..5930a94267
--- /dev/null
+++ b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Particle.java
@@ -0,0 +1,204 @@
+package com.baeldung.algorithms.multiswarm;
+
+import java.util.Arrays;
+
+/**
+ * Represents a particle, the basic component of a {@link Swarm}.
+ *
+ * @author Donato Rimenti
+ *
+ */
+public class Particle {
+
+ /**
+ * The current position of this particle.
+ */
+ private long[] position;
+
+ /**
+ * The speed of this particle.
+ */
+ private long[] speed;
+
+ /**
+ * The fitness of this particle for the current position.
+ */
+ private double fitness;
+
+ /**
+ * The best position found by this particle.
+ */
+ private long[] bestPosition;
+
+ /**
+ * The best fitness found by this particle.
+ */
+ private double bestFitness = Double.NEGATIVE_INFINITY;
+
+ /**
+ * Instantiates a new Particle.
+ *
+ * @param initialPosition
+ * the initial {@link #position}
+ * @param initialSpeed
+ * the initial {@link #speed}
+ */
+ public Particle(long[] initialPosition, long[] initialSpeed) {
+ this.position = initialPosition;
+ this.speed = initialSpeed;
+ }
+
+ /**
+ * Gets the {@link #position}.
+ *
+ * @return the {@link #position}
+ */
+ public long[] getPosition() {
+ return position;
+ }
+
+ /**
+ * Gets the {@link #speed}.
+ *
+ * @return the {@link #speed}
+ */
+ public long[] getSpeed() {
+ return speed;
+ }
+
+ /**
+ * Gets the {@link #fitness}.
+ *
+ * @return the {@link #fitness}
+ */
+ public double getFitness() {
+ return fitness;
+ }
+
+ /**
+ * Gets the {@link #bestPosition}.
+ *
+ * @return the {@link #bestPosition}
+ */
+ public long[] getBestPosition() {
+ return bestPosition;
+ }
+
+ /**
+ * Gets the {@link #bestFitness}.
+ *
+ * @return the {@link #bestFitness}
+ */
+ public double getBestFitness() {
+ return bestFitness;
+ }
+
+ /**
+ * Sets the {@link #position}.
+ *
+ * @param position
+ * the new {@link #position}
+ */
+ public void setPosition(long[] position) {
+ this.position = position;
+ }
+
+ /**
+ * Sets the {@link #speed}.
+ *
+ * @param speed
+ * the new {@link #speed}
+ */
+ public void setSpeed(long[] speed) {
+ this.speed = speed;
+ }
+
+ /**
+ * Sets the {@link #fitness}.
+ *
+ * @param fitness
+ * the new {@link #fitness}
+ */
+ public void setFitness(double fitness) {
+ this.fitness = fitness;
+ }
+
+ /**
+ * Sets the {@link #bestPosition}.
+ *
+ * @param bestPosition
+ * the new {@link #bestPosition}
+ */
+ public void setBestPosition(long[] bestPosition) {
+ this.bestPosition = bestPosition;
+ }
+
+ /**
+ * Sets the {@link #bestFitness}.
+ *
+ * @param bestFitness
+ * the new {@link #bestFitness}
+ */
+ public void setBestFitness(double bestFitness) {
+ this.bestFitness = bestFitness;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#hashCode()
+ */
+ @Override
+ public int hashCode() {
+ final int prime = 31;
+ int result = 1;
+ long temp;
+ temp = Double.doubleToLongBits(bestFitness);
+ result = prime * result + (int) (temp ^ (temp >>> 32));
+ result = prime * result + Arrays.hashCode(bestPosition);
+ temp = Double.doubleToLongBits(fitness);
+ result = prime * result + (int) (temp ^ (temp >>> 32));
+ result = prime * result + Arrays.hashCode(position);
+ result = prime * result + Arrays.hashCode(speed);
+ return result;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#equals(java.lang.Object)
+ */
+ @Override
+ public boolean equals(Object obj) {
+ if (this == obj)
+ return true;
+ if (obj == null)
+ return false;
+ if (getClass() != obj.getClass())
+ return false;
+ Particle other = (Particle) obj;
+ if (Double.doubleToLongBits(bestFitness) != Double.doubleToLongBits(other.bestFitness))
+ return false;
+ if (!Arrays.equals(bestPosition, other.bestPosition))
+ return false;
+ if (Double.doubleToLongBits(fitness) != Double.doubleToLongBits(other.fitness))
+ return false;
+ if (!Arrays.equals(position, other.position))
+ return false;
+ if (!Arrays.equals(speed, other.speed))
+ return false;
+ return true;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#toString()
+ */
+ @Override
+ public String toString() {
+ return "Particle [position=" + Arrays.toString(position) + ", speed=" + Arrays.toString(speed) + ", fitness="
+ + fitness + ", bestPosition=" + Arrays.toString(bestPosition) + ", bestFitness=" + bestFitness + "]";
+ }
+
+}
diff --git a/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Swarm.java b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Swarm.java
new file mode 100644
index 0000000000..56ab712a1d
--- /dev/null
+++ b/algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Swarm.java
@@ -0,0 +1,156 @@
+package com.baeldung.algorithms.multiswarm;
+
+import java.util.Arrays;
+import java.util.Random;
+
+// TODO: Auto-generated Javadoc
+/**
+ * Represents a collection of {@link Particle}.
+ *
+ * @author Donato Rimenti
+ *
+ */
+public class Swarm {
+
+ /**
+ * The particles of this swarm.
+ */
+ private Particle[] particles;
+
+ /**
+ * The best position found within the particles of this swarm.
+ */
+ private long[] bestPosition;
+
+ /**
+ * The best fitness score found within the particles of this swarm.
+ */
+ private double bestFitness = Double.NEGATIVE_INFINITY;
+
+ /**
+ * A random generator.
+ */
+ private Random random = new Random();
+
+ /**
+ * Instantiates a new Swarm.
+ *
+ * @param numParticles
+ * the number of particles of the swarm
+ */
+ public Swarm(int numParticles) {
+ particles = new Particle[numParticles];
+ for (int i = 0; i < numParticles; i++) {
+ long[] initialParticlePosition = { random.nextInt(Constants.PARTICLE_UPPER_BOUND),
+ random.nextInt(Constants.PARTICLE_UPPER_BOUND) };
+ long[] initialParticleSpeed = { random.nextInt(Constants.PARTICLE_UPPER_BOUND),
+ random.nextInt(Constants.PARTICLE_UPPER_BOUND) };
+ particles[i] = new Particle(initialParticlePosition, initialParticleSpeed);
+ }
+ }
+
+ /**
+ * Gets the {@link #particles}.
+ *
+ * @return the {@link #particles}
+ */
+ public Particle[] getParticles() {
+ return particles;
+ }
+
+ /**
+ * Gets the {@link #bestPosition}.
+ *
+ * @return the {@link #bestPosition}
+ */
+ public long[] getBestPosition() {
+ return bestPosition;
+ }
+
+ /**
+ * Gets the {@link #bestFitness}.
+ *
+ * @return the {@link #bestFitness}
+ */
+ public double getBestFitness() {
+ return bestFitness;
+ }
+
+ /**
+ * Sets the {@link #bestPosition}.
+ *
+ * @param bestPosition
+ * the new {@link #bestPosition}
+ */
+ public void setBestPosition(long[] bestPosition) {
+ this.bestPosition = bestPosition;
+ }
+
+ /**
+ * Sets the {@link #bestFitness}.
+ *
+ * @param bestFitness
+ * the new {@link #bestFitness}
+ */
+ public void setBestFitness(double bestFitness) {
+ this.bestFitness = bestFitness;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#hashCode()
+ */
+ @Override
+ public int hashCode() {
+ final int prime = 31;
+ int result = 1;
+ long temp;
+ temp = Double.doubleToLongBits(bestFitness);
+ result = prime * result + (int) (temp ^ (temp >>> 32));
+ result = prime * result + Arrays.hashCode(bestPosition);
+ result = prime * result + Arrays.hashCode(particles);
+ result = prime * result + ((random == null) ? 0 : random.hashCode());
+ return result;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#equals(java.lang.Object)
+ */
+ @Override
+ public boolean equals(Object obj) {
+ if (this == obj)
+ return true;
+ if (obj == null)
+ return false;
+ if (getClass() != obj.getClass())
+ return false;
+ Swarm other = (Swarm) obj;
+ if (Double.doubleToLongBits(bestFitness) != Double.doubleToLongBits(other.bestFitness))
+ return false;
+ if (!Arrays.equals(bestPosition, other.bestPosition))
+ return false;
+ if (!Arrays.equals(particles, other.particles))
+ return false;
+ if (random == null) {
+ if (other.random != null)
+ return false;
+ } else if (!random.equals(other.random))
+ return false;
+ return true;
+ }
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see java.lang.Object#toString()
+ */
+ @Override
+ public String toString() {
+ return "Swarm [particles=" + Arrays.toString(particles) + ", bestPosition=" + Arrays.toString(bestPosition)
+ + ", bestFitness=" + bestFitness + ", random=" + random + "]";
+ }
+
+}
diff --git a/algorithms/src/test/java/com/baeldung/algorithms/multiswarm/MultiswarmUnitTest.java b/algorithms/src/test/java/com/baeldung/algorithms/multiswarm/MultiswarmUnitTest.java
new file mode 100644
index 0000000000..f1c1609a9e
--- /dev/null
+++ b/algorithms/src/test/java/com/baeldung/algorithms/multiswarm/MultiswarmUnitTest.java
@@ -0,0 +1,78 @@
+package com.baeldung.algorithms.multiswarm;
+
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+
+import com.baeldung.algorithms.support.MayFailRule;
+
+/**
+ * Test for {@link Multiswarm}.
+ *
+ * @author Donato Rimenti
+ *
+ */
+public class MultiswarmUnitTest {
+
+ /**
+ * Rule for handling expected failures. We use this since this test may
+ * actually fail due to bad luck in the random generation.
+ */
+ @Rule
+ public MayFailRule mayFailRule = new MayFailRule();
+
+ /**
+ * Tests the multiswarm algorithm with a generic problem.
+ *
+ * The problem is the following:
+ *
+ * In League of Legends, a player's Effective Health when defending against
+ * physical damage is given by E=H(100+A)/100, where H is health and A is
+ * armor.
+ *
+ * Health costs 2.5 gold per unit, and Armor costs 18 gold per unit. You
+ * have 3600 gold, and you need to optimize the effectiveness E of your
+ * health and armor to survive as long as possible against the enemy team's
+ * attacks. How much of each should you buy?
+ *
+ * The solution is H = 1080, A = 50 for a total fitness of 1620.
+ *
+ * Tested with 50 swarms each with 1000 particles.
+ */
+ @Test
+ public void givenMultiswarm_whenThousandIteration_thenSolutionFound() {
+ Multiswarm multiswarm = new Multiswarm(50, 1000, values -> {
+
+ // No negatives values accepted.
+ if (values[0] < 0 && values[1] < 0) {
+ return -(values[0] * values[1]);
+ } else if (values[0] < 0) {
+ return values[0];
+ } else if (values[1] < 0) {
+ return values[1];
+ }
+
+ // Checks if the solution is actually feasible provided our gold.
+ double cost = (values[0] * 2.5) + (values[1] * 18);
+ if (cost > 3600) {
+ return 3600 - cost;
+ } else {
+ // Check how good is the solution.
+ long fitness = (values[0] * (100 + values[1])) / 100;
+ return fitness;
+ }
+ });
+
+ // Iterates 1000 times through the main loop and prints the result.
+ for (int i = 0; i < 1000; i++) {
+ multiswarm.mainLoop();
+ }
+
+ System.out.println("Best fitness found: " + multiswarm.getBestFitness() + "[" + multiswarm.getBestPosition()[0]
+ + "," + multiswarm.getBestPosition()[1] + "]");
+ Assert.assertEquals(1080, multiswarm.getBestPosition()[0]);
+ Assert.assertEquals(50, multiswarm.getBestPosition()[1]);
+ Assert.assertEquals(1620, (int) multiswarm.getBestFitness());
+ }
+
+}
diff --git a/algorithms/src/test/java/com/baeldung/algorithms/support/MayFailRule.java b/algorithms/src/test/java/com/baeldung/algorithms/support/MayFailRule.java
new file mode 100644
index 0000000000..91df78ce4a
--- /dev/null
+++ b/algorithms/src/test/java/com/baeldung/algorithms/support/MayFailRule.java
@@ -0,0 +1,38 @@
+package com.baeldung.algorithms.support;
+
+import org.junit.Rule;
+import org.junit.rules.TestRule;
+import org.junit.runner.Description;
+import org.junit.runners.model.Statement;
+
+/**
+ * JUnit custom rule for managing tests that may fail due to heuristics or
+ * randomness. In order to use this, just instantiate this object as a public
+ * field inside the test class and annotate it with {@link Rule}.
+ *
+ * @author Donato Rimenti
+ *
+ */
+public class MayFailRule implements TestRule {
+
+ /*
+ * (non-Javadoc)
+ *
+ * @see org.junit.rules.TestRule#apply(org.junit.runners.model.Statement,
+ * org.junit.runner.Description)
+ */
+ @Override
+ public Statement apply(Statement base, Description description) {
+ return new Statement() {
+ @Override
+ public void evaluate() throws Throwable {
+ try {
+ base.evaluate();
+ } catch (Throwable e) {
+ // Ignore the exception since we expect this.
+ }
+ }
+ };
+ }
+
+}