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From "Roman Werpachowski (JIRA)" <>
Subject [jira] Commented: (MATH-373) StatUtils.sum returns NaN for zero-length arrays
Date Fri, 11 Jun 2010 12:39:13 GMT


Roman Werpachowski commented on MATH-373:

Speaking as a maintainer of client code which uses ACM, I'd rather cope with occasional incompatibilities
in the same packages, than have to change ALL my client code to keep up with the package name
changes after every release. A reason to change the package name would be if you wanted to
use the old and new version side by side, but that would not be a common usage pattern for
ACM, I think.

> StatUtils.sum returns NaN for zero-length arrays
> ------------------------------------------------
>                 Key: MATH-373
>                 URL:
>             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
> 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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