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

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.

Version:

$Revision: 628352 $ $Date: 2008-02-16 09:39:03 -0700 (Sat, 16 Feb 2008) $

See Also:

Serialized Form

Constructor Summary

GeometricMean()
Create a GeometricMean instance

GeometricMean(SumOfLogs sumOfLogs)
Create a GeometricMean instance using the given SumOfLogs instance

Method Summary

void	clear() Clears the internal state of the Statistic
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

test

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GeometricMean

public GeometricMean()

Create a GeometricMean instance

GeometricMean

public GeometricMean(SumOfLogs sumOfLogs)

Create a GeometricMean instance using the given SumOfLogs instance

Method Detail

increment

public void increment(double d)

Description copied from interface: StorelessUnivariateStatistic

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.

See Also:

StorelessUnivariateStatistic.increment(double)

getResult

public double getResult()

Description copied from interface: StorelessUnivariateStatistic

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.

See Also:

StorelessUnivariateStatistic.getResult()

clear

public void clear()

Description copied from interface: StorelessUnivariateStatistic

Clears the internal state of the Statistic

Specified by:

clear in interface StorelessUnivariateStatistic

Specified by:

clear in class AbstractStorelessUnivariateStatistic

See Also:

StorelessUnivariateStatistic.clear()

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()

Description copied from interface: StorelessUnivariateStatistic

Returns the number of values that have been added.

Returns:

the number of values.

See Also:

StorelessUnivariateStatistic.getN()

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