[jira] Resolved: (MATH-221) Result of multiplying and equals for complex numbers is wrong

["Luc Maisonobe (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-221?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Luc Maisonobe resolved MATH-221.
--------------------------------

    Resolution: Fixed

According to IEEE-754 (the standard that specifies double number representation), 0 is a signed value, so there are two different representations: +0 and -0, and there is a specific rule that say these two representations should always compare as equal.

The fact the multiplication returns a real part as -0 is therefore correct behavior. The fact it is not equal to another value where +0 appears was an error in out implementation of the equal method.

The problem has been fixed in the subversion repository (in branch 2.0) as of r690308.


> Result of multiplying and equals for complex numbers is wrong
> -------------------------------------------------------------
>
>                 Key: MATH-221
>                 URL: https://issues.apache.org/jira/browse/MATH-221
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 1.2
>         Environment: OS: Debian lenny
> IDE: Eclipse; Version: 3.4.0; Build id: I20080617-2000
> java.runtime.version=1.6.0_04-b12
> java.vendor.url=http://java.sun.com/
>            Reporter: Dieter Roth
>            Priority: Minor
>
> Hi.
> The bug relates on complex numbers.
> The methods "multiply" and "equals" of the class Complex are involved.
> mathematic background:  (0,i) * (-1,0i) = (0,-i).
> little java program + output that shows the bug:
> -----------------------------------------------------------------------
> {code}
> import org.apache.commons.math.complex.*;
> public class TestProg {
>         public static void main(String[] args) {
>                 ComplexFormat f = new ComplexFormat();
>                 Complex c1 = new Complex(0,1);
>                 Complex c2 = new Complex(-1,0);
>                 Complex res = c1.multiply(c2);
>                 Complex comp = new Complex(0,-1);
>                 System.out.println("res:  "+f.format(res));
>                 System.out.println("comp: "+f.format(comp));
>                 System.out.println("res=comp: "+res.equals(comp));
>         }
> }
> {code}
> -----------------------------------------------------------------------
> res:  -0 - 1i
> comp: 0 - 1i
> res=comp: false
> -----------------------------------------------------------------------
> I think the "equals" should return "true".
> The problem could either be the "multiply" method that gives (-0,-1i) instead of (0,-1i),
> or if you think thats right, the equals method has to be modified.
> Good Luck
> Dieter

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