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Cc: freebsd-numerics@freebsd.org
Subject: Re: Complex arg-trig functions
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On 09/18/2012 01:19 AM, Bruce Evans wrote:
> On Mon, 17 Sep 2012, Stephen Montgomery-Smith wrote:

>> I don't think your code works.  It should be ry = atan2f(2, -ay) / 2,
>> not ry = atan2f(2, ay) / 2.
>
> Only logically.  As I explained, the negation makes no difference to the
> result, but of course takes longer, so I removed it.

No, they give different results.  atan2(y,x) = Pi - atan2(y,-x) if y is 
positive.