Обсуждение: Documentation fix regarding atan2

On Wed, Sep 05, 2007 at 10:37:18 +1000,
  Andrew Maclean <andrew.amaclean@gmail.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.

Bruno Wolff III <bruno@wolff.to> writes:
>  Andrew Maclean <andrew.amaclean@gmail.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?

They're logically equivalent but I think Andrew is right that y/x
corresponds to the usual interpretation of X and Y directions in
trigonometry.

            regards, tom lane

Change made.  Thanks.  Your documentation changes can be viewed in five
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---------------------------------------------------------------------------


Andrew Maclean 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
>
> This looks to be the standard C++/c atan2(y,x) function.
>
> 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)).
> So it must be degrees(atan2(y,x))=degrees(atan2(2,1))=63.4.
>
>
> Thanks
>    Andrew
>
> --
> ___________________________________________
> Andrew J. P. Maclean
> Centre for Autonomous Systems
> The Rose Street Building J04
> The University of Sydney  2006  NSW
> AUSTRALIA
> Ph: +61 2 9351 3283
> Fax: +61 2 9351 7474
> URL: http://www.acfr.usyd.edu.au/
> ___________________________________________

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  Bruce Momjian  <bruce@momjian.us>          http://momjian.us
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Thanks.




--
___________________________________________
Andrew J. P. Maclean
Centre for Autonomous Systems
The Rose Street Building J04
The University of Sydney  2006  NSW
AUSTRALIA
Ph: +61 2 9351 3283
Fax: +61 2 9351 7474
URL: http://www.acfr.usyd.edu.au/
___________________________________________