Mailing-List: contact issues-help@commons.apache.org; run by ezmlm
Precedence: bulk
Reply-To: issues@commons.apache.org
Date: Fri, 22 Jun 2012 06:06:43 +0000 (UTC)
From: =?utf-8?Q?S=C3=A9bastien_Brisard_=28JIRA=29?= <jira@apache.org>
To: issues@commons.apache.org
Message-ID: <220713578.42945.1340345203682.JavaMail.jiratomcat@issues-vm>
In-Reply-To: <665728963.588.1339267902813.JavaMail.jiratomcat@issues-vm>
Subject: [jira] [Updated] (MATH-803) Bugs in
 RealVector.ebeMultiply(RealVector) and ebeDivide(RealVector)
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable


     [ https://issues.apache.org/jira/browse/MATH-803?page=3Dcom.atlassian.=
jira.plugin.system.issuetabpanels:all-tabpanel ]

S=C3=A9bastien Brisard updated MATH-803:
-----------------------------------

    Summary: Bugs in RealVector.ebeMultiply(RealVector) and ebeDivide(RealV=
ector)  (was: Bugs in OpenMapRealVector.ebeMultiply(RealVector) and ebeDivi=
de(RealVector))

Changed the title of the ticket, since the scope of this bug is much broade=
r. Indeed, it affects {{RealVector.ebeMultiply(RealVector)}} and {{RealVect=
or.ebeDivide(RealVector)}} as soon as the {{RealVector}} passed as a parame=
ter is sparse, see examples below
# for {{ebeMultiply()}}
{code:java}
final RealVector v1 =3D new ArrayRealVector(new double[] { 1d });
final RealVector v2 =3D new OpenMapRealVector(new double[] { -0d });
final RealVector w =3D 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 =3D new ArrayRealVector(new double[] { 1d });
final RealVector v2 =3D new OpenMapRealVector(new double[] { -0d });
final RealVector w =3D v1.ebeDivide(v2);
System.out.println(w.getEntry(0));
{code}
prints {{Infinity}}, instead of {{-Infinity}}.

               =20
> 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: S=C3=A9bastien Brisard
>            Assignee: S=C3=A9bastien Brisard
>
> {{OpenMapRealVector.ebeMultiply(RealVector)}} and {{OpenMapRealVector.ebe=
Divide(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 =3D new OpenMapRealVector(this);
>         Iterator iter =3D 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 =3D=3D 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* entrie=
s of v (instead of those entries which correspond to non-zero entries of th=
is). I'm afraid about performance losses.

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