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From Sébastien Brisard (JIRA) <j...@apache.org>
Subject [jira] [Commented] (MATH-803) Bugs in RealVector.ebeMultiply(RealVector) and ebeDivide(RealVector)
Date Fri, 22 Jun 2012 06:10:42 GMT

    [ https://issues.apache.org/jira/browse/MATH-803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13399150#comment-13399150
] 

Sébastien Brisard commented on MATH-803:
----------------------------------------

According to this [thread|http://markmail.org/thread/4evd6dcyrh2yc2bs], {{ebeMultiply}} and
{{ebeDivide}} are deprecated.
                
> Bugs in RealVector.ebeMultiply(RealVector) and ebeDivide(RealVector)
> --------------------------------------------------------------------
>
>                 Key: MATH-803
>                 URL: https://issues.apache.org/jira/browse/MATH-803
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>            Reporter: Sébastien Brisard
>            Assignee: Sébastien Brisard
>
> {{OpenMapRealVector.ebeMultiply(RealVector)}} and {{OpenMapRealVector.ebeDivide(RealVector)}}
return wrong values when one entry of the specified {{RealVector}} is nan or infinity. The
bug is easy to understand. Here is the current implementation of {{ebeMultiply}}
> {code:java}
>     public OpenMapRealVector ebeMultiply(RealVector v) {
>         checkVectorDimensions(v.getDimension());
>         OpenMapRealVector res = new OpenMapRealVector(this);
>         Iterator iter = entries.iterator();
>         while (iter.hasNext()) {
>             iter.advance();
>             res.setEntry(iter.key(), iter.value() * v.getEntry(iter.key()));
>         }
>         return res;
>     }
> {code}
> The assumption is that for any double {{x}}, {{x * 0d == 0d}} holds, which is not true.
The bug is easy enough to identify, but more complex to solve. The only solution I can come
up with is to loop through *all* entries of v (instead of those entries which correspond to
non-zero entries of this). I'm afraid about performance losses.

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