opendial.bn.distribs.densityfunctions

Class DiscreteDensityFunction

java.lang.Object

opendial.bn.distribs.densityfunctions.DiscreteDensityFunction

All Implemented Interfaces:

DensityFunction

public class DiscreteDensityFunction
extends java.lang.Object
implements DensityFunction

Density function defined via a set of discrete points. The density at a given point x is defined as the probability mass for the closest point y in the distribution, divided by a constant volume (used for normalisation).

Field Summary

Fields

Modifier and Type	Field and Description
static java.util.logging.Logger	log

Constructor Summary

Constructors

Constructor and Description
DiscreteDensityFunction(java.util.Map<double[],java.lang.Double> points) Creates a new discrete density function, given the set of points

Method Summary

Modifier and Type	Method and Description
DiscreteDensityFunction	copy() Returns a copy of the density function
java.util.Map<double[],java.lang.Double>	discretise(int nbBuckets) Returns the points for this distribution.
java.util.List<org.w3c.dom.Element>	generateXML(org.w3c.dom.Document doc) Returns the XML representation (as a list of XML elements) of the density function
double	getCDF(double... x) Returns the cumulative distribution for the distribution (by counting all the points with a value that is lower than x).
double	getDensity(double... x) Returns the density for a given point.
int	getDimensions() Returns the dimensionality of the distribution.
double[]	getMean() Returns the means of the distribution (calculated like for a categorical distribution).
double[]	getVariance() Returns the variance of the distribution (calculated like for a categorical distribution)
int	hashCode() Returns the hashcode for the function
double[]	sample() Samples according to the density function
java.lang.String	toString() Returns a pretty print representation of the function

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

log

public static final java.util.logging.Logger log

Constructor Detail

DiscreteDensityFunction

public DiscreteDensityFunction(java.util.Map<double[],java.lang.Double> points)

Creates a new discrete density function, given the set of points

Parameters:

points - a set of (value,prob) pairs

Method Detail

getDensity

public double getDensity(double... x)

Returns the density for a given point. The density is derived in two steps:

1. locating the point in the distribution that is closest to x (according to Euclidian distance)
2. dividing the probability mass for the point by the n-dimensional volume around this point. The radius of the ball is the half of the minimum distance between the points of the distribution.

Specified by:

getDensity in interface DensityFunction

Parameters:

x - the point

Returns:

the density at the point

sample

public double[] sample()

Samples according to the density function

Specified by:

sample in interface DensityFunction

Returns:

the resulting sample

discretise

public java.util.Map<double[],java.lang.Double> discretise(int nbBuckets)

Returns the points for this distribution.

Specified by:

discretise in interface DensityFunction

Parameters:

nbBuckets - the number of discretisation buckets

Returns:

a discretised probability distribution, mapping a collection of points to a probability value

copy

public DiscreteDensityFunction copy()

Returns a copy of the density function

Specified by:

copy in interface DensityFunction

Returns:

the copy

toString

public java.lang.String toString()

Returns a pretty print representation of the function

Overrides:

toString in class java.lang.Object

Returns:

the pretty print

hashCode

public int hashCode()

Returns the hashcode for the function

Overrides:

hashCode in class java.lang.Object

Returns:

the hashcode

getDimensions

public int getDimensions()

Returns the dimensionality of the distribution.

Specified by:

getDimensions in interface DensityFunction

Returns:

the dimensionality.

getMean

public double[] getMean()

Returns the means of the distribution (calculated like for a categorical distribution).

Specified by:

getMean in interface DensityFunction

Returns:

the density mean.

getVariance

public double[] getVariance()

Returns the variance of the distribution (calculated like for a categorical distribution)

Specified by:

getVariance in interface DensityFunction

Returns:

the density variance

getCDF

public double getCDF(double... x)

Returns the cumulative distribution for the distribution (by counting all the points with a value that is lower than x).

Specified by:

getCDF in interface DensityFunction

Parameters:

x - the (possibly multivariate) point x

Returns:

the cumulative probability from 0 to x extracted

generateXML

public java.util.List<org.w3c.dom.Element> generateXML(org.w3c.dom.Document doc)

Description copied from interface: DensityFunction

Returns the XML representation (as a list of XML elements) of the density function

Specified by:

generateXML in interface DensityFunction

Parameters:

doc - the XML document for the node

Returns:

the corresponding XML elements