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From "Roman Werpachowski (JIRA)" <j...@apache.org>
Subject [jira] Created: (MATH-373) StatUtils.sum returns NaN for zero-length arrays
Date Mon, 07 Jun 2010 14:55:44 GMT
StatUtils.sum returns NaN for zero-length arrays
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                 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


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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