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From: Ada novice <ycalleecharan@gmx.com>
Newsgroups: comp.lang.ada
Subject: Re: Arctan: to use with single or with double arguments?
Date: Sat, 25 Sep 2010 01:44:15 -0700 (PDT)
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On Sep 24, 11:55=A0pm, Jeffrey Carter
<spam.jrcarter....@spam.not.acm.org> wrote:
> On 09/24/2010 02:32 PM, Ada novice wrote:
>
>
>
> > Now I know that Arctan(Y, X) =A0gives the result between -pi to pi whil=
e
> > Arctan(Y / X) =A0gives the result between -pi/2 to pi/2.
>
> There is no one-parameter Arctan defined in
> Ada.Numerics.Generic_Elementary_Functions; the parameter X has a default =
of 1.0,
> so what you're really calling is
>
> Arctan (Y / X, 1.0);
>

Thanks. This is true. The default value is 1.0 .



> Since the X parameter is positive, it's clear the result will be in quadr=
ant I
> or IV, or -Pi/2 to Pi/2. Giving both parameters thus seems more accurate,=
 as it
> correctly handles cases in all 4 quadrants. In addition, it is defined fo=
r X =3D
> 0.0 (except when Y =3D 0.0).
>
> HTH.

I understand that using Arctan (Y, X) gives the right quadrant. And
the sine of the
Arctan result will depend on the quadrant location of (X, Y). The case
with Arctan (Y/X, 1.0) gives
the principal value of the Arctan function i.e. between -pi/2 and pi/
2.

In my expression: Z =3D Force * Sin (A) then it was unclear to me if A
in Sin (A) should be limited to -pi/2 to
pi/2 or can can it from to -pi to pi.