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Date: Thu, 17 Apr 2014 11:15:16 +0000 (UTC)
From: "Gilles (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Message-ID: <JIRA.12708189.1397455482559.131705.1397733316780@arcas>
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Subject: [jira] [Comment Edited] (MATH-1118) Complex: semantics of equals !=
 Double equals, mismatch with hashCode
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    [ https://issues.apache.org/jira/browse/MATH-1118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13972842#comment-13972842 ] 

Gilles edited comment on MATH-1118 at 4/17/14 11:14 AM:
--------------------------------------------------------

Uploaded patch for making "equals" compatible with "hashCode" and adding new "equals" methods for testing floating-point equality (using implementations in "o.a.c.m.util.Precision").

OK to commit?


was (Author: erans):
Uploaded patch for making "equals" compatible with "hashCode" and adding
new "equals" methods for testing floating equality (using implementations in "o.a.c.m.util.Precision").

OK to commit?

> Complex: semantics of equals != Double equals, mismatch with hashCode
> ---------------------------------------------------------------------
>
>                 Key: MATH-1118
>                 URL: https://issues.apache.org/jira/browse/MATH-1118
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.2
>         Environment: Mac OS 10.9, Java 6, 7
>            Reporter: Cyrille Artho
>         Attachments: MATH-1118.patch, MATH-1118.patch, Report5.java, Report5a.java
>
>
> Two complex numbers with real/imaginary parts 0.0d but different signs compare as equal numbers. This is according to their mathematical value; the comparison is done via 
>                 return (real == c.real) && (imaginary == c.imaginary);
> Unfortunately, two Double values do NOT compare as equal in that case, so real.equals(c.real) would return false if the signs differ.
> This becomes a problem because for the hashCode, MathUtils.hash is used on the real and imaginary parts, which in turn uses Double.hash.
> This violates the contract on equals/hashCode, so Complex numbers cannot be used in a hashtable or similar data structure:
>     Complex c1 = new Complex(0.0, 0.0);
>     Complex c2 = new Complex(0.0, -0.0);
>     // Checks the contract:  equals-hashcode on c1 and c2
>     assertTrue("Contract failed: equals-hashcode on c1 and c2", c1.equals(c2) ? c1.hashCode() == c2.hashCode() : true);


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