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Improved efficiency of evaluate method. 

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@522305 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Phil Steitz 2007-03-25 17:26:35 +00:00
parent 35af6fe1d2
commit cc6c1f22e9
1 changed files with 7 additions and 6 deletions
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13
src/java/org/apache/commons/math/stat/descriptive/moment/Variance.java
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@ -255,17 +255,18 @@ public class Variance extends AbstractStorelessUnivariateStatistic implements Se
var = 0.0;
} else if (length > 1) {
double accum = 0.0;
double dev = 0.0;
double accum2 = 0.0;
for (int i = begin; i < begin + length; i++) {
accum += Math.pow((values[i] - mean), 2.0);
accum2 += (values[i] - mean);
dev = values[i] - mean;
accum += dev * dev;
accum2 += dev;
}
double len = (double) length;
if (isBiasCorrected) {
var = (accum - (Math.pow(accum2, 2) / ((double) length))) /
(double) (length - 1);
var = (accum - (accum2 * accum2 / len)) / (len - 1.0);
} else {
var = (accum - (Math.pow(accum2, 2) / ((double) length))) /
(double) length;
var = (accum - (accum2 * accum2 / len)) / len;
}
}
}