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https://issues.apache.org/jira/browse/MATH-373?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bill Barker updated MATH-373:
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Fix Version/s: 3.0
The consensus of the commons-math developers is that, since the current
behavior is documented in 2.x, that this will have to wait for 3.0. Fixing
this would introduce a too large incompatibility change to include in 2.x.
I can attach a patch against 2.x that fixes this, as long as anybody using the
patch understands that it isn't supported.
> 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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