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

java.lang.Object
  extended by org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic
      extended by org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic
          extended by 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,

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

Field Summary
private static long serialVersionUID
          Serializable version identifier
private  StorelessUnivariateStatistic sumOfLogs
          Wrapped SumOfLogs instance
 
Constructor Summary
GeometricMean()
          Create a GeometricMean instance
GeometricMean(SumOfLogs sumOfLogs)
          Create a GeometricMean instance using the given SumOfLogs instance
 
Method Summary
private  void checkEmpty()
          Throws IllegalStateException if n > 0.
 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
 

Field Detail

serialVersionUID

private static final long serialVersionUID
Serializable version identifier

See Also:
Constant Field Values

sumOfLogs

private StorelessUnivariateStatistic sumOfLogs
Wrapped SumOfLogs instance

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

checkEmpty

private void checkEmpty()
Throws IllegalStateException if n > 0.