Bernoulli.html

Bernoulli.java

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package blog.distrib;

import blog.*;
import java.util.*;
import common.Util;

A distribution over Boolean values. It is defined by one parameter, which is the probability of true. This parameter can be specified when the distribution is initialized, in which case the distribution takes no arguments; or the distribution can be initialized with no parameters, in which case it takes the probability as an argument.


public class Bernoulli extends AbstractCondProbDistrib {

Creates a new Bernoulli distribution with the probability of true set to pi.


    public Bernoulli(double pi) {
	fixedParam = true;
	setSuccessProb(pi);
    }

Creates a new Bernoulli distribution. If params is empty, then the distribution takes one CPD argument, which is the probability of true. Otherwise, params should contain one element, a Number specifying this probability.


    public Bernoulli( List params ){
	if (params.size() == 0) {
	    fixedParam = false;
	} else if (params.size() == 1) {
	    fixedParam = true;
	    Object paramObj = params.get(0);
	    if (!(paramObj instanceof Number)) {
		throw new IllegalArgumentException
		    ("Parameter to Bernoulli distrib must be of class " 
		     + "Number, not " + paramObj.getClass() + ".");
	    }
	    
	    pi = ((Number) paramObj).doubleValue();
	    setSuccessProb(pi);
	} else {
	    throw new IllegalArgumentException
		("Bernoulli distribution takes at most one parameter.");
	}
    }

Returns the probability of the given Boolean value under this distribution. This method should only be called if this distribution was initialized with a fixed success probability, or if ensureProbsInited has just been called.


    public double getProb(boolean value) {
	if (value) {
	    return pi;
	}

	return (1 - pi);
    }

    public double getProb( List args, Object value ) {
	ensureParamsInited(args);

	if (!(value instanceof Boolean)) {
	    throw new IllegalArgumentException
		("Bernoulli distribution is over objects of class Boolean, "
		 + "not " + value.getClass() + ".");
	}

	return getProb(((Boolean) value).booleanValue());
    }

Returns the log probability of the given Boolean value under this distribution. This method should only be called if this distribution was initialized with a fixed success probability, or if ensureProbsInited has just been called.


    public double getLogProb(boolean value) {
	if (value) {
	    return Math.log(pi);
	}

	return Math.log(1 - pi);
    }

Returns a boolean value sampled from this distribution. This method should only be called if this distribution was initialized with a fixed success probability, or if ensureProbsInited has just been called.


    public boolean sampleVal() {
	if (Util.random() < pi) {
	    return true;
	}
	return false;
    }

    public Object sampleVal( List args, Type childType ) {
	ensureParamsInited(args);
	return Boolean.valueOf(sampleVal());
    }
    
    private void ensureParamsInited(List args) {
	if (fixedParam) {
	    if (!args.isEmpty()) {
		throw new IllegalArgumentException
		    ("Bernoulli distribution with fixed success probability "
		     + "expects no arguments.");
	    }
	} else {
	    if (args.size() != 1) {
		throw new IllegalArgumentException
		    ("Bernoulli distribution without fixed success "
		     + "probability expects exactly one argument, specifying "
		     + "that probability.");
	    }
	    Object paramObj = args.get(0);
	    if (!(paramObj instanceof Number)) {
		throw new IllegalArgumentException
		    ("Parameter to Bernoulli distrib must be of class " 
		     + "Number, not " + paramObj.getClass() + ".");
	    }
	    setSuccessProb(((Number) paramObj).doubleValue());
	}
    }

    private void setSuccessProb(double pi) {
	if ((pi < 0) || (pi > 1)) {
	    throw new IllegalArgumentException
		("Parameter to Bernoulli must be in interval [0, 1], not " 
		 + pi + ".");
	}

	this.pi = pi;
    }

    private boolean fixedParam;
    private double pi;
}

This file was generated on Tue Jun 08 17:53:47 PDT 2010 from file Bernoulli.java
by the ilog.language.tools.Hilite Java tool written by Hassan Aït-Kaci