[jira] [Updated] (MATH-803) Bugs in RealVector.ebeMultiply(RealVector) and ebeDivide(RealVector)

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

     [ https://issues.apache.org/jira/browse/MATH-803?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sébastien Brisard updated MATH-803:
-----------------------------------

    Summary: Bugs in RealVector.ebeMultiply(RealVector) and ebeDivide(RealVector)  (was: Bugs in OpenMapRealVector.ebeMultiply(RealVector) and ebeDivide(RealVector))

Changed the title of the ticket, since the scope of this bug is much broader. Indeed, it affects {{RealVector.ebeMultiply(RealVector)}} and {{RealVector.ebeDivide(RealVector)}} as soon as the {{RealVector}} passed as a parameter is sparse, see examples below
# for {{ebeMultiply()}}
{code:java}
final RealVector v1 = new ArrayRealVector(new double[] { 1d });
final RealVector v2 = new OpenMapRealVector(new double[] { -0d });
final RealVector w = v1.ebeMultiply(v2);
System.out.println(1d / w.getEntry(0));
{code}
prints {{Infinity}}, instead of {{-Infinity}} (because the sign is lost in {{v2}}). This means that {{w}} holds {{+0d}} instead of {{-0d}}.
# for {{ebeDivide()}}
{code:java}
final RealVector v1 = new ArrayRealVector(new double[] { 1d });
final RealVector v2 = new OpenMapRealVector(new double[] { -0d });
final RealVector w = v1.ebeDivide(v2);
System.out.println(w.getEntry(0));
{code}
prints {{Infinity}}, instead of {{-Infinity}}.

                
> 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.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira