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Bill Barker commented on MATH373:

As Gilles mentioned, changing the package name for commonsmath was discussed and voted on
for 2.x. The result of the vote was to keep the package name, since commonsmath won't usually
be provided by a third party library. Since nothing much has changed, I can't see that commonsmath
would change it's package for version 3.0.
> StatUtils.sum returns NaN for zerolength arrays
> 
>
> Key: MATH373
> URL: https://issues.apache.org/jira/browse/MATH373
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 2.1
> Reporter: Roman Werpachowski
> Fix For: 3.0
>
>
> StatUtils.sum returns NaN for zerolength arrays, which is:
> 1. inconsistent with the mathematical notion of sum: in maths, sum_{i=0}^{N1} a_i will
be 0 for N=0. In particular, the identity
> sum_{i=0}^{k1} a_i + sum_{i=k}^{N1} = sum_{i=0}^{N1}
> 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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