From: | Bruno Wolff III <bruno(at)wolff(dot)to> |
---|---|
To: | a(dot)maclean(at)cas(dot)edu(dot)au |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Documentation fix regarding atan2 |
Date: | 2007-09-05 02:33:41 |
Message-ID: | 20070905023341.GA28376@wolff.to |
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Lists: | pgsql-general |
On Wed, Sep 05, 2007 at 10:37:18 +1000,
Andrew Maclean <andrew(dot)amaclean(at)gmail(dot)com> wrote:
> In Table 9.4 of the documentation atan2 is described as follows:
> atan2(*x*, *y*) inverse tangent of *x*/*y*
>
> I am sure it should read as:
> atan2(*y*, x) inverse tangent of y/x
Aren't those two statements sayiong the same thing?
You've just switched the names 'x' and 'y' and not changed their relationships.
>
>
> You can easily test this:
> If y = 2, x = 1, then degrees(atan(y/x)) =63.4 but if we proceed according
> to the documentation; degrees(atan2(x,y))=degrees(atan2(1,2))=25.6 which is
> not the same as degrees(atan(y/x)).
In this example you switched things around part way thorugh. atan2(1,2)
is the atan of (1/2), not atan(2/1) as used at the beginning of the example.
> So it must be degrees(atan2(y,x))=degrees(atan2(2,1))=63.4.
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