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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-370) NaN in "equals" methods
Date Sat, 08 May 2010 14:01:51 GMT

    [ https://issues.apache.org/jira/browse/MATH-370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12865468#action_12865468
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Phil Steitz commented on MATH-370:
----------------------------------

The method Mathutils.equals(double, double) was implemented for the reason that in some cases,
users may wish to treat doubles with NaN values as equal.  The internal classes that use it
are the equals methods for statistics and statistical aggregates.  When these classes were
defined, we decided that we would treat two statistics or statistical aggregates as equal
iff they had the same values, including NaNs.  So for example, two StatisticalSummaryValues
instances are equal iff they report the same values for all statistics, with NaNs treated
as "the same value."  The MathUtils.equals(double, double) method was introduced as a convenience
method to do this kind of comparison.  I guess we could (deprecate and) change the name if
it makes it look like all of our computations are defining equals that way, which is certainly
not the case.  In general, we do try to follow IEEE754.  We agreed early on that we would
carefully document how NaNs are treated throughout Commons Math.  We have slipped a little
over the years, but in the case of this method and the classes that use it, the documentation
is clear.

Sorry I misunderstood the point of the issue here.  I now get your point that naming the method
"equals" makes it look like we are re-defining equals for primitive doubles, which is not
our intent.  So maybe we deprecate the equals method and rename something like "equalsIncludingNaN"
or something simpler?

> NaN in "equals" methods
> -----------------------
>
>                 Key: MATH-370
>                 URL: https://issues.apache.org/jira/browse/MATH-370
>             Project: Commons Math
>          Issue Type: Bug
>            Reporter: Gilles
>            Priority: Minor
>
> In "MathUtils", some "equals" methods will return true if both argument are NaN.
> Unless I'm mistaken, this contradicts the IEEE standard.
> If nobody objects, I'm going to make the changes.

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