org.apache.commons.math.stat.descriptive.moment

Class GeometricMean

java.lang.Object

org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic

org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic

org.apache.commons.math.stat.descriptive.moment.GeometricMean

All Implemented Interfaces:

java.io.Serializable, StorelessUnivariateStatistic, UnivariateStatistic

public class GeometricMean
extends AbstractStorelessUnivariateStatistic
implements java.io.Serializable

Returns the geometric mean of the available values.

Uses a SumOfLogs instance to compute sum of logs and returns exp( 1/n (sum of logs) ). Therefore,

• If any of values are < 0, the result is NaN.
• If all values are non-negative and less than Double.POSITIVE_INFINITY, but at least one value is 0, the result is 0.
• If both Double.POSITIVE_INFINITY and Double.NEGATIVE_INFINITY are among the values, the result is NaN.

Note that this implementation is not synchronized. If multiple threads access an instance of this class concurrently, and at least one of the threads invokes the increment() or clear() method, it must be synchronized externally.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
GeometricMean() Create a GeometricMean instance
GeometricMean(GeometricMean original) Copy constructor, creates a new GeometricMean identical to the original
GeometricMean(SumOfLogs sumOfLogs) Create a GeometricMean instance using the given SumOfLogs instance

Method Summary

Modifier and Type	Method and Description
void	clear() Clears the internal state of the Statistic
GeometricMean	copy() Returns a copy of the statistic with the same internal state.
static void	copy(GeometricMean source, GeometricMean dest) Copies source to dest.
double	evaluate(double[] values, int begin, int length) Returns the geometric mean of the entries in the specified portion of the input array.
long	getN() Returns the number of values that have been added.
double	getResult() Returns the current value of the Statistic.
StorelessUnivariateStatistic	getSumLogImpl() Returns the currently configured sum of logs implementation
void	increment(double d) Updates the internal state of the statistic to reflect the addition of the new value.
void	setSumLogImpl(StorelessUnivariateStatistic sumLogImpl) Sets the implementation for the sum of logs.

Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic

equals, evaluate, hashCode, incrementAll, incrementAll

Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic

evaluate, getData, setData, setData

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GeometricMean

public GeometricMean()

Create a GeometricMean instance

GeometricMean

public GeometricMean(GeometricMean original)

Copy constructor, creates a new GeometricMean identical to the original

Parameters:

original - the GeometricMean instance to copy

GeometricMean

public GeometricMean(SumOfLogs sumOfLogs)

Create a GeometricMean instance using the given SumOfLogs instance

Parameters:

sumOfLogs - sum of logs instance to use for computation

Method Detail

copy

public GeometricMean copy()

Returns a copy of the statistic with the same internal state.

Specified by:

copy in interface StorelessUnivariateStatistic

Specified by:

copy in interface UnivariateStatistic

Specified by:

copy in class AbstractStorelessUnivariateStatistic

Returns:

a copy of the statistic

increment

public void increment(double d)

Updates the internal state of the statistic to reflect the addition of the new value.

Specified by:

increment in interface StorelessUnivariateStatistic

Specified by:

increment in class AbstractStorelessUnivariateStatistic

Parameters:

d - the new value.

getResult

public double getResult()

Returns the current value of the Statistic.

Specified by:

getResult in interface StorelessUnivariateStatistic

Specified by:

getResult in class AbstractStorelessUnivariateStatistic

Returns:

value of the statistic, Double.NaN if it has been cleared or just instantiated.

clear

public void clear()

Clears the internal state of the Statistic

Specified by:

clear in interface StorelessUnivariateStatistic

Specified by:

clear in class AbstractStorelessUnivariateStatistic

evaluate

public double evaluate(double[] values,
                       int begin,
                       int length)

Returns the geometric mean of the entries in the specified portion of the input array.

See GeometricMean for details on the computing algorithm.

Throws IllegalArgumentException if the array is null.

Specified by:

evaluate in interface UnivariateStatistic

Overrides:

evaluate in class AbstractStorelessUnivariateStatistic

Parameters:

values - input array containing the values

begin - first array element to include

length - the number of elements to include

Returns:

the geometric mean or Double.NaN if length = 0 or any of the values are <= 0.

Throws:

java.lang.IllegalArgumentException - if the input array is null or the array index parameters are not valid

See Also:

UnivariateStatistic.evaluate(double[], int, int)

getN

public long getN()

Returns the number of values that have been added.

Specified by:

getN in interface StorelessUnivariateStatistic

Returns:

the number of values.

setSumLogImpl

public void setSumLogImpl(StorelessUnivariateStatistic sumLogImpl)

Sets the implementation for the sum of logs.

This method must be activated before any data has been added - i.e., before increment has been used to add data; otherwise an IllegalStateException will be thrown.

Parameters:

sumLogImpl - the StorelessUnivariateStatistic instance to use for computing the log sum

Throws:

java.lang.IllegalStateException - if data has already been added (i.e if n > 0)

getSumLogImpl

public StorelessUnivariateStatistic getSumLogImpl()

Returns the currently configured sum of logs implementation

Returns:

the StorelessUnivariateStatistic implementing the log sum

copy

public static void copy(GeometricMean source,
                        GeometricMean dest)

Copies source to dest.

Neither source nor dest can be null.

Parameters:

source - GeometricMean to copy

dest - GeometricMean to copy to

Throws:

java.lang.NullPointerException - if either source or dest is null