[jira] [Resolved] (MATH-812) In RealVector, dotProduct and outerProduct return wrong results due to misuse of sparse iterators

["Sébastien Brisard (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-812?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sébastien Brisard resolved MATH-812.
------------------------------------

    Resolution: Fixed

Unit tests now pass, at the price of a performance loss.
                
> 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
>              Labels: linear, sparse
>             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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