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From Sébastien Brisard (JIRA) <j...@apache.org>
Subject [jira] [Created] (MATH-812) In RealVector, dotProduct and outerProduct return wrong results due to misuse of sparse iterators
Date Sat, 07 Jul 2012 12:02:34 GMT
Sébastien Brisard created MATH-812:
--------------------------------------

             Summary: In RealVector, dotProduct and outerProduct return wrong results due
to misuse of sparse iterators
                 Key: MATH-812
                 URL: https://issues.apache.org/jira/browse/MATH-812
             Project: Commons Math
          Issue Type: Bug
    Affects Versions: 3.0
            Reporter: Sébastien Brisard
            Assignee: Sébastien Brisard
             Fix For: 3.1


In class {{RealVector}}, the default implementation of {{RealMatrix outerProduct(RealVector)}}
uses sparse iterators on the entries of the two vectors. The rationale behind this is that
{{0d * x == 0d}} is {{true}} for all {{double x}}. This assumption is in fact false, since
{{0d * NaN == NaN}}.

Proposed fix is to loop through *all* entries of both vectors. This can have a significant
impact on the CPU cost, but robustness should probably be preferred over speed in default
implementations.

Same issue occurs with {{double dotProduct(RealVector)}}, which uses sparse iterators for
{{this}} only.

Another option would be to through an exception if {{isNaN()}} is {{true}}, in which case
caching could be used for both {{isNaN()}} and {{isInfinite()}}.

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