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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-632) NaN: Method "equals" in Complex not consistent with "==" for "double" primitive type
Date Sun, 24 Jul 2011 22:13:11 GMT

    [ https://issues.apache.org/jira/browse/MATH-632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13070265#comment-13070265
] 

Phil Steitz commented on MATH-632:
----------------------------------

Can anyone present a practical argument for changing the current documented behavior of Complex.equals?
 There is no perfect solution here, given the way equals is defined for doubles in Java. 
The current behavior is simple, well-documented and has been defined this way since version
1.0.  Changing it may break some code that depends on it, so we need to have good practical
reasons to change. 

> NaN: Method "equals" in Complex not consistent with "==" for "double" primitive type
> ------------------------------------------------------------------------------------
>
>                 Key: MATH-632
>                 URL: https://issues.apache.org/jira/browse/MATH-632
>             Project: Commons Math
>          Issue Type: Bug
>            Reporter: Gilles
>            Priority: Minor
>             Fix For: 3.0
>
>
> The following tests show several contradictions:
> {code}
> final double a = Double.NaN;
> final double b = Double.NaN;
> Assert.assertFalse("a == b", a == b); // (1)
> Assert.assertEquals("a != b", a, b, Double.MIN_VALUE); // (2)
> Assert.assertFalse("a == b", MathUtils.equals(a, b, Double.MIN_VALUE)); // (3)
> Assert.assertFalse("a == b", MathUtils.equals(a, b, Double.MIN_VALUE)); // (4)
> final Double dA = Double.valueOf(a);
> final Double dB = Double.valueOf(b);
> Assert.assertFalse("dA == dB", dA.doubleValue() == dB.doubleValue()); // (5)
> Assert.assertTrue("!dA.equals(dB)", dA.equals(dB)); // (6)
> final Complex cA = new Complex(a, 0);
> final Complex cB = new Complex(b, 0);
> Assert.assertTrue("!cA.equals(cB)", cA.equals(cB));  // (7)
> {code}
> They all pass; thus:
> # "Double" does not behave as "double": (1) and (5) vs (6)
> # Two NaNs are almost equal for Junit: (2)
> # Two NaNs are never equal for MathUtils: (3) and (4)
> # Complex.NaN is consistent with Object "Double.valueOf(NaN)" (hence not with primitive
"Double.NaN"): (7)
> This is quite confusing.
> In MathUtils, we chose to follow IEEE754 (and Java for primitive "double"), i.e. it is
"correct" that assertion (1) is false. Do we want "Complex" to conform with this or with the
inconsistent behaviour of "Double"?

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