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Date: Sat, 7 Jul 2012 12:30:35 +0000 (UTC)
From: "Gilles (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
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Subject: [jira] [Commented] (MATH-812) In RealVector, dotProduct and
 outerProduct return wrong results due to misuse of sparse iterators
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    [ https://issues.apache.org/jira/browse/MATH-812?page=3Dcom.atlassian.j=
ira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D134086=
51#comment-13408651 ]=20

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

bq. [...] robustness should probably be preferred over speed in default imp=
lementations.

+1

               =20
> In RealVector, dotProduct and outerProduct return wrong results due to mi=
suse 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=C3=A9bastien Brisard
>            Assignee: S=C3=A9bastien Brisard
>              Labels: linear, sparse
>             Fix For: 3.1
>
>
> In class {{RealVector}}, the default implementation of {{RealMatrix outer=
Product(RealVector)}} uses sparse iterators on the entries of the two vecto=
rs. The rationale behind this is that {{0d * x =3D=3D 0d}} is {{true}} for =
all {{double x}}. This assumption is in fact false, since {{0d * NaN =3D=3D=
 NaN}}.
> Proposed fix is to loop through *all* entries of both vectors. This can h=
ave 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 spar=
se 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 {{isInfinit=
e()}}.

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