Particle.java 

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package blog;

import java.util.*;

import common.Util;
A Particle for Particle Filtering. The particle is advanced as it receives evidence and queries with calls to methods { Providing evidence also reweights the particle according to it. A method {

Link:  #take(Evidence)} and {@link #answerQueries(Collection)}., #copy()} can be used for resampling. 


public class Particle {
Creates a new particle. numTimeSlicesInMemory indicates how many time slices need to be kept in memory. The properties table specifies configuration parameters. 


    public Particle(Set idTypes, int numTimeSlicesInMemory) {
	this.numTimeSlicesInMemory = numTimeSlicesInMemory;
	this.idTypes = idTypes;
	curWorld = new DefaultPartialWorld(idTypes);
	weight = -1;
    }
Takes evidence relative to some new time step, updates current world based on it, and recalculates particle weight according to its probability. 


    public void take(Evidence evidence) {
	setValues(evidence);
	ensureVariablesAreSupported(evidence.getEvidenceVars());
	weight = evidence.getEvidenceProb(curWorld);
    }
Takes a collection of queries and answers them based on current world. 


    public void answerQueries(Collection queries) {
	Collection queriesVars = getQueriesVars(queries);
	includeDerivedAmongVars(queriesVars);
	ensureVariablesAreSupported(queriesVars);
	updateQueriesStats(queries);
    }
Sets given evidence in current world. 


    private void setValues(Evidence evidence) {
	for (Iterator iter = evidence.getEvidenceVars().iterator(); iter.hasNext(); ) {
	    BayesNetVar var = (BayesNetVar) iter.next();
	    if (var instanceof DerivedVar)
		curWorld.addDerivedVar((DerivedVar) var);
	    else
		curWorld.setValue((BasicVar) var, evidence.getObservedValue(var));
	}
    }

    public PartialWorld getLatestWorld() {
	if (curWorld == null) {
	    throw new IllegalStateException
	    ("Particle has no latest sample.");
	}
	return curWorld;
    }

    public double getLatestWeight() {
	if (weight == -1) {
	    throw new IllegalStateException
		("Particle has no latest sample.");
	}
	return weight;
    }
Includes in current world the variables which are derived variables in given collection. 


    private void includeDerivedAmongVars(Collection vars) {
	for (Iterator iter = vars.iterator(); iter.hasNext(); ) {
	    BayesNetVar var = (BayesNetVar) iter.next();
	    if (var instanceof DerivedVar)
		curWorld.addDerivedVar((DerivedVar) var);
	}
    }
Ensure given variables are supported in current world. 


    private void ensureVariablesAreSupported(Collection vars) {
	InstantiatingEvalContext context 
	    = new InstantiatingEvalContext(curWorld);
	for (Iterator iter = vars.iterator(); iter.hasNext(); ) {
	    BayesNetVar var = (BayesNetVar) iter.next();
	    var.ensureDetAndSupported(context);
	}
    }

    private Collection getQueriesVars(Collection queries) {
	Collection result = new LinkedList();
	for (Iterator iter = queries.iterator(); iter.hasNext(); ) {
	    result.addAll(((Query) iter.next()).getVariables());
	}
	return result;
    }

    public Particle copy() {
	Particle copy = new Particle(idTypes, numTimeSlicesInMemory);
	DefaultPartialWorld newWorld = (DefaultPartialWorld) ((DefaultPartialWorld)curWorld).clone();
	copy.setWorld(newWorld);
	copy.weight = weight;
	return copy;
    }

    protected void setWorld(PartialWorld curWorld) {
	this.curWorld = curWorld;
    }

    public void updateQueriesStats(Collection queries) {
	if(getLatestWeight() > 0) {
	    for(Iterator iter = queries.iterator(); iter.hasNext(); ) {
		Query q = (Query) iter.next();
		q.updateStats(getLatestWorld(), getLatestWeight());
	    }
	}
    }

    private Set idTypes; // of Type
    private PartialWorld curWorld = null;
    private double weight = -1;
    public int numTimeSlicesInMemory;
}

This file was generated on Tue Jun 08 17:53:36 PDT 2010 from file Particle.java
by the ilog.language.tools.Hilite Java tool written by Hassan Aït-Kaci