[jira] Commented: (MATH-163) The evaluate method and the getResult method of class Variance give different results

["Rory Winston (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MATH-163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12485214 ] 

Rory Winston commented on MATH-163:
-----------------------------------

I guess the correct answer is Inf - although I can see that some other packages return NaN. For instance in R:

> x=c(1.0,2.0,Inf)
> var(x)
[1] NaN


> The evaluate method and the getResult method of class Variance give different results
> -------------------------------------------------------------------------------------
>
>                 Key: MATH-163
>                 URL: https://issues.apache.org/jira/browse/MATH-163
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 1.1
>            Reporter: Nele Smeets
>
> Consider the following test code:
>   // construct an array of input values, containing infinity  
>   double[] values = new double[] {1.0, 2.0, Double.POSITIVE_INFINITY};
>   // find the variance using Variance.evaluate(double[])
>   Variance var1 = new Variance();
>   double value1 = var1.evaluate(values);
>   // find the variance using Variance.getResult()
>   Variance var2 = new Variance();
>   var2.incrementAll(values);
>   double value2 = var2.getResult();
>   // print out the results
>   System.out.println(value1);
>   System.out.println(value2);
> This code prints out:
> NaN
> Infinity
> So, we get two different variances, depending on the method we use. 
> (The same is true when we use Double.NEGATIVE_INFINITY as input value instead of Double.POSITIVE_INFINITY.)

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