org.apache.commons.math3.stat.descriptive.moment
Class GeometricMean

java.lang.Object
  extended by org.apache.commons.math3.stat.descriptive.AbstractUnivariateStatistic
      extended by org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic
          extended by org.apache.commons.math3.stat.descriptive.moment.GeometricMean
All Implemented Interfaces:
Serializable, StorelessUnivariateStatistic, UnivariateStatistic, MathArrays.Function

public class GeometricMean
extends AbstractStorelessUnivariateStatistic
implements 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,

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:
$Id: GeometricMean.java 1416643 2012-12-03 19:37:14Z tn $
See Also:
Serialized Form

Constructor Summary
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
 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.math3.stat.descriptive.AbstractStorelessUnivariateStatistic
equals, evaluate, hashCode, incrementAll, incrementAll
 
Methods inherited from class org.apache.commons.math3.stat.descriptive.AbstractUnivariateStatistic
evaluate, getData, getDataRef, setData, setData, test, test, test, 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(GeometricMean original)
              throws NullArgumentException
Copy constructor, creates a new GeometricMean identical to the original

Parameters:
original - the GeometricMean instance to copy
Throws:
NullArgumentException - if original is null

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)
                throws MathIllegalArgumentException
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
Specified by:
evaluate in interface MathArrays.Function
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:
MathIllegalArgumentException - 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)
                   throws MathIllegalStateException

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:
MathIllegalStateException - 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)
                 throws NullArgumentException
Copies source to dest.

Neither source nor dest can be null.

Parameters:
source - GeometricMean to copy
dest - GeometricMean to copy to
Throws:
NullArgumentException - if either source or dest is null


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