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From "Bill Barker (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-373) StatUtils.sum returns NaN for zero-length arrays
Date Sat, 12 Jun 2010 04:05:13 GMT

    [ https://issues.apache.org/jira/browse/MATH-373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12878204#action_12878204
] 

Bill Barker commented on MATH-373:
----------------------------------

As Gilles mentioned, changing the package name for commons-math was discussed and voted on
for 2.x.  The result of the vote was to keep the package name, since commons-math won't usually
be provided by a third party library.  Since nothing much has changed, I can't see that commons-math
would change it's package for version 3.0.

> StatUtils.sum returns NaN for zero-length arrays
> ------------------------------------------------
>
>                 Key: MATH-373
>                 URL: https://issues.apache.org/jira/browse/MATH-373
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 2.1
>            Reporter: Roman Werpachowski
>             Fix For: 3.0
>
>
> StatUtils.sum returns NaN for zero-length arrays, which is:
> 1. inconsistent with the mathematical notion of sum: in maths, sum_{i=0}^{N-1} a_i will
be 0 for N=0. In particular, the identity
> sum_{i=0}^{k-1} a_i + sum_{i=k}^{N-1} = sum_{i=0}^{N-1}
> is broken for k = 0, since NaN + x = NaN, not x.
> 2. introduces hard to debug erros (returning a NaN is one of the worst forms of reporting
an exceptional condition, as NaNs propagate silently and require manual tracing during the
debugging)
> 3. enforces "special case" handling when the user expects that the summed array can have
a zero length.
> The correct behaviour is, in my opinion, to return 0.0, not NaN in the above case.

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