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[Octave-bug-tracker] [bug #45339] sind, cosd don't do range reduction ac
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From: |
Charles Karney |
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Subject: |
[Octave-bug-tracker] [bug #45339] sind, cosd don't do range reduction accurately |
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Date: |
Wed, 04 May 2016 12:26:03 +0000 |
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User-agent: |
Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:46.0) Gecko/20100101 Firefox/46.0 |
Follow-up Comment #4, bug #45339 (project octave):
I've checked the specifications of sinPi, cosPi, atan2Pi in IEEE Std 754
2008. I recommend making sind, cosd, atan2d behave in compatible ways
(and I don't think that the patches I provided ensure this).
Specifically
[sind is odd]
sind(n*180) = -0 if n is a negative integer
sind(n*180) = +0 if n is a positive integer
sind(+/-0) = +/-0
[cosd is even]
cosd(n*180+90) = +0 for all integer n
[symmetries of atan2d]
atan2d(+/-0, -0) = +/-180
atan2d(+/-0, +0) = +/-0
atan2d(+/-0, x) = +/-180 for x < 0
atan2d(+/-0, x) = +/-0 for x > 0
and similar special cases for x or y = +/-inf
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