commonSense.stat.basic
Class SecondMoment

java.lang.Object
  extended byorg.apache.commons.math.stat.univariate.AbstractUnivariateStatistic
      extended byorg.apache.commons.math.stat.univariate.AbstractStorelessUnivariateStatistic
          extended bycommonSense.stat.basic.FirstMoment
              extended bycommonSense.stat.basic.SecondMoment
All Implemented Interfaces:
java.io.Serializable, org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic, org.apache.commons.math.stat.univariate.UnivariateStatistic
Direct Known Subclasses:
ThirdMoment

public class SecondMoment
extends FirstMoment
implements java.io.Serializable

Computes a statistic related to the Second Central Moment. Specifically, what is computed is the sum of squared deviations from the sample mean.

The following recursive updating formula is used:

Let

Then

new value = old value + dev^2 * (n -1) / n.

Returns Double.NaN if no data values have been added and returns 0 if there is just one value in the data set.

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: 1.20 $ $Date: 2004/07/18 05:39:30 $
See Also:
Serialized Form

Field Summary
protected  double m2
          second moment of values that have been added
 
Fields inherited from class commonSense.stat.basic.FirstMoment
dev, m1, n, nDev
 
Constructor Summary
SecondMoment()
          Create a SecondMoment instance
 
Method Summary
 void clear()
           
 double getResult()
           
 void increment(double d)
           
 
Methods inherited from class commonSense.stat.basic.FirstMoment
getN
 
Methods inherited from class org.apache.commons.math.stat.univariate.AbstractStorelessUnivariateStatistic
equals, evaluate, evaluate, hashCode, incrementAll, incrementAll
 
Methods inherited from class org.apache.commons.math.stat.univariate.AbstractUnivariateStatistic
test
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

m2

protected double m2
second moment of values that have been added

Constructor Detail

SecondMoment

public SecondMoment()
Create a SecondMoment instance

Method Detail

increment

public void increment(double d)
Specified by:
increment in interface org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic
Overrides:
increment in class FirstMoment
See Also:
StorelessUnivariateStatistic.increment(double)

clear

public void clear()
Specified by:
clear in interface org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic
Overrides:
clear in class FirstMoment
See Also:
StorelessUnivariateStatistic.clear()

getResult

public double getResult()
Specified by:
getResult in interface org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic
Overrides:
getResult in class FirstMoment
See Also:
StorelessUnivariateStatistic.getResult()


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