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https://issues.apache.org/jira/browse/MATH-1113?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13946880#comment-13946880
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Gilles commented on MATH-1113:
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bq. both "FastMath.atan2" and "FastMath.atan" call the internal method
Yes, that's the correct statement. Sorry.
I agree with the explanation.
I should have stated the issue differently: If "FastMath" is a faster "Math",
then it can never be slower.
In another library, there is a version of "atan2" that is much faster than
"FastMath.atan2"; it internally calls "Math.atan".
So the question is eventually: Why is "FastMath.atan" significantly slower than
"Math.atan"?
If there is no way for performance improvement while sticking to the stated
accuracy (by tweaking the current code), we should think about renaming the
class. We should also figure out how to allow users to trade off accuracy for
speed.
It's a pity that application developers must be careful of which "Math" methods
there are going to replace with the "FastMath" equivalent.
And "atan" is not the worst case...
> "FastMath.atan" is slow
> -----------------------
>
> Key: MATH-1113
> URL: https://issues.apache.org/jira/browse/MATH-1113
> Project: Commons Math
> Issue Type: Improvement
> Affects Versions: 3.2
> Reporter: Gilles
> Priority: Minor
> Labels: perfomance
> Fix For: 3.3
>
>
> This issue is related to
> MATH-740
> MATH-901
> Micro-benchmarks show that "FastMath.atan2" is faster than "Math.atan2" but
> that "FastMath.atan" is slower than "Math.atan". However, both
> "FastMath.atan2" and "Math.atan" call the internal method
> "FastMath.atan(double,double,boolean)".
> It seems that some performance improvement could be achieved, through
> understanding why the results seem contradictory.
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