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https://issues.apache.org/jira/browse/MATH-370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12869542#action_12869542
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Gilles commented on MATH-370:
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> [...] Regarding equals(double, double), I don't see why we need that at all
> [...]
As I noted in the previous comment, this version of an equality test seems to
make sense, from a numerical perspective, if it's implemented by using the
"equals(double,double,int)" method (introduced according to
[MATH-264|https://issues.apache.org/jira/browse/MATH-264]) where the third
argument is set to 1): It means that there is no floating point number in the
range of real numbers defined by the first and second arguments.
Practically, I've now modified all the "equals" methods (so that NaN != NaN)
and for each one, I've also implemented an "equalsIncludingNaN" version (for
which NaN == NaN).
In the "stat" package, wherever "equals" was used, I replaced it with
"equalsIncludingNaN".
I modified the junit tests ("mutatis mutandis") and they all pass.
I don't think it's worth waiting v3.0 to introduce those changes, for the
following reasons:
# The change is non-breaking wrt usage of the code in package "stat", or any
other code that was using "equals".
# No functionality is removed (i.e. the "equalsIncludingNaN" provide the same
behaviour as previously provided by the corresponding "equals" methods).
# For a direct user of "equals", the change is, in principle, breaking but only
in the single case where he relies on NaNs being equal. How likely is it that
expecting such a behaviour is *not* wrong (i.e. comparing the results of
computations that produced meaningless values)?
To further alleviate the (marginal) risk of the last point, couldn't we make a
poll on the "user" ML, so that people can make a case if they really need the
time to a major version change in order to adapt to this modification?
> 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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