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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MATH-1118) Complex: semantics of equals != Double equals, mismatch with hashCode
Date Mon, 14 Apr 2014 13:13:15 GMT

     [ https://issues.apache.org/jira/browse/MATH-1118?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Gilles updated MATH-1118:
-------------------------

    Attachment: MATH-1118.patch

Patch: proposed change (with one failing test).


> 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, 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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