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Improved javadoc, simplified implementation, ensured NaN is returned when n=0. 

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@141336 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Phil Steitz 2004-06-26 22:41:27 +00:00
parent 51ca427022
commit 653035b434
1 changed files with 10 additions and 32 deletions
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42
src/java/org/apache/commons/math/stat/univariate/moment/StandardDeviation.java
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@ -18,19 +18,16 @@ package org.apache.commons.math.stat.univariate.moment;
import java.io.Serializable;
/**
* Computes the sample standard deviation. The standard deviation
* is the positive square root of the variance. See {@link Variance} for
* more information.
*
* @version $Revision: 1.17 $ $Date: 2004/06/23 16:26:15 $
* @version $Revision: 1.18 $ $Date: 2004/06/26 22:41:27 $
*/
public class StandardDeviation extends Variance implements Serializable {
/** Serializable version identifier */
static final long serialVersionUID = 5728716329662425188L;
/** */
protected double std = Double.NaN;
/** */
private double lastVar = 0.0;
/**
* Constructs a StandardDeviation
@ -40,7 +37,8 @@ public class StandardDeviation extends Variance implements Serializable {
}
/**
* Constructs a StandardDeviation with an external moment
* Constructs a StandardDeviation from an external second moment.
*
* @param m2 the external moment
*/
public StandardDeviation(final SecondMoment m2) {
@ -58,17 +56,7 @@ public class StandardDeviation extends Variance implements Serializable {
* @see org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic#getResult()
*/
public double getResult() {
if (lastVar != super.getResult()) {
lastVar = super.getResult();
if (Double.isNaN(lastVar)) {
std = Double.NaN;
} else if (lastVar == 0.0) {
std = 0.0;
} else {
std = Math.sqrt(lastVar);
}
}
return std;
return Math.sqrt(super.getResult());
}
/**
@ -76,11 +64,11 @@ public class StandardDeviation extends Variance implements Serializable {
*/
public void clear() {
super.clear();
lastVar = 0.0;
}
/**
* Returns the Standard Deviation on an array of values.
*
* @param values Is a double[] containing the values
* @param begin processing at this point in the array
* @param length the number of elements to include
@ -88,18 +76,8 @@ public class StandardDeviation extends Variance implements Serializable {
* or 0.0 for a single value set.
* @see org.apache.commons.math.stat.univariate.UnivariateStatistic#evaluate(double[], int, int)
*/
public double evaluate(
final double[] values,
final int begin,
final int length) {
double var = super.evaluate(values, begin, length);
if (Double.isNaN(var)) {
return Double.NaN;
}
return var != 0.0 ? Math.sqrt(var) : 0.0;
public double evaluate(final double[] values, final int begin, final int length) {
return Math.sqrt(super.evaluate(values, begin, length));
}
}