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From "Rob Tompkins (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MATH-1398) Support simple Arithmetic mean without Compute correction factor in second pass?
Date Tue, 18 Apr 2017 15:20:41 GMT
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[ https://issues.apache.org/jira/browse/MATH-1398?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Rob Tompkins updated MATH-1398:
-------------------------------
Fix Version/s: 4.X

> Support simple Arithmetic mean without Compute correction factor in second pass?
> --------------------------------------------------------------------------------
>
>                 Key: MATH-1398
>                 URL: https://issues.apache.org/jira/browse/MATH-1398
>             Project: Commons Math
>          Issue Type: Improvement
>         Environment: All
>            Reporter: Francis Li
>              Labels: easyfix
>             Fix For: 4.X
>
>
> The mean calculate by this function is different excel.  which just sum/n as first half
of function. can we provide another option to calculate normal means?
> org.apache.commons.math3.stat.descriptive.moment.Mean
> public double evaluate(final double[] values,final int begin, final int length)
> 163    throws MathIllegalArgumentException {
> 164        if (test(values, begin, length)) {
> 165            Sum sum = new Sum();
> 166            double sampleSize = length;
> 167
> 168            // Compute initial estimate using definitional formula
> 169            double xbar = sum.evaluate(values, begin, length) / sampleSize;
> 170
> 171            // Compute correction factor in second pass
> 172            double correction = 0;
> 173            for (int i = begin; i < begin + length; i++) {
> 174                correction += values[i] - xbar;
> 175            }
> 176            return xbar + (correction/sampleSize);
> 177        }
> 178        return Double.NaN;
> 179    }

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