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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-812) In RealVector, dotProduct and outerProduct return wrong results due to misuse of sparse iterators
Date Sat, 07 Jul 2012 12:30:35 GMT

    [ https://issues.apache.org/jira/browse/MATH-812?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13408651#comment-13408651
] 

Gilles commented on MATH-812:
-----------------------------

bq. [...] robustness should probably be preferred over speed in default implementations.

+1

                
> 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: S├ębastien Brisard
>            Assignee: S├ębastien 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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