particleupdaterepulsive.java

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package net.sourceforge.jswarm_pso;

/**
 * Particle update strategy 
 * Warning: It's designed to be used with SwarmRepulsive swarms
 * 
 * @author Pablo Cingolani <[e-mail]>
 */
public class ParticleUpdateRepulsive extends ParticleUpdate {
	
	/** Random vector for local update */
	double rlocal[];
	/** Random vector for global update */
	double rother[];
	/** Random factor for random velocity update */
	double randRand;

	/**
	 * Constructor 
	 * @param particle : Sample of particles that will be updated later
	 */
	public ParticleUpdateRepulsive(Particle particle) {
		super(particle);
		rlocal = new double[particle.getDimention()];
		rother = new double[particle.getDimention()];
	}
	
	/** 
	 * This method is called at the begining of each iteration
	 * Initialize random vectors use for local and global updates (rlocal[] and rother[])
	 */
	public void begin(Swarm swarm) {
		randRand = Math.random();// Random factor for random velocity

		int i,dim = swarm.getSampleParticle().getDimention();
		for( i=0 ; i < dim ; i++ ) {
			rlocal[i] = Math.random();
			rother[i] = Math.random();
		}
	}
	
	/**
	 * Update particle's position and velocity using repulsive algorithm
	 */
	public void update(Swarm swarm, Particle particle) {
		double position[] = particle.getPosition();
		double velocity[] = particle.getVelocity();
		double particleBestPosition[] = particle.getBestPosition();
		double maxVelocity[] = swarm.getMaxVelocity();
		double minVelocity[] = swarm.getMinVelocity();
		SwarmRepulsive swarmRepulsive = (SwarmRepulsive)swarm;

		// Randomly select other particle
		int randOtherParticle = (int) (Math.random() * swarm.size());
		double otherParticleBestPosition[] = swarm.getParticle(randOtherParticle).getBestPosition(); 

		// Update velocity and position
		for( int i = 0; i < position.length; i++ ) {
			// Update position
			position[i] = position[i] + velocity[i];

			// Create a random velocity (one on every dimention)
			double randVelocity = velocity[i] = (maxVelocity[i] - minVelocity[i]) * Math.random() + minVelocity[i];

			// Update velocity
			velocity[i] = swarmRepulsive.getInertia() * velocity[i] // Inertia
					+ rlocal[i] * swarmRepulsive.getParticleIncrement() * (particleBestPosition[i] - position[i]) // Local best
					+ rother[i] * swarmRepulsive.getOtherParticleIncrement() * (otherParticleBestPosition[i] - position[i]) // other Particle Best Position
					+ randRand * swarmRepulsive.getRandomIncrement() * randVelocity; // Random velocity
		}
	}
}