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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada 95 ARCTAN function
Newsgroups: comp.lang.ada
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Date: Thu, 1 Mar 2007 20:43:20 +0100
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Date: 2007-03-01T20:43:07+01:00
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On 1 Mar 2007 10:58:25 -0800, saag wrote:

> Does the ARCTAN(y,x) function in the ADA.NUMERICS package provide the
> same results an atan2 function call in c?  I'm trying to find out if
> Ada supplies an atan2 function (that gives an appropriate answer based
> on the quadrant the original point lies in)

A.5.1 (11) states that arctan (y, x) yields the result in the quadrant of
the point (x,y). I.e. (with circle=2pi)

       |    y>0    |    y<0
-------+-----------+----------
x>0    |  0..pi/2  | -pi/2..0
       |           |
x<0    |  pi/2..pi | -pi..-pi/2

When x is negative and y is approaches 0 changing its sign, it gets
instable (either pi or -pi). Argument_Error is propagated when x and y are
0.

(I cannot tell how this corresponds to the semantics of atan2)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de