[
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
