Re: documentation bug: atan2

[Ansley Manke <ansley@xxxxxxxxxxxxx>]

Hi everyone,
Thanks Andrew for pointing this out.  You're correct, and this has been
corrected in the HTML Users Guide.

Ansley Manke

Andrew Wittenberg wrote:

> Hello again,
>
> Many of you have probably already figured this out... it appears that in
> the Ferret v5.22 documentation for atan2, the arguments X,Y are swapped
> compared to what Ferret actually does.  The Fortran and Matlab versions of
> ATAN2 are consistent with the Ferret program, so I believe the
> documentation (not the program) should be changed (see details below).
>
> Cheers,
>
> Andrew
>
> ----------------------------------------------------------------------
> Andrew Wittenberg          Program in Atmospheric and Oceanic Sciences
> andyw@splash.princeton.edu                        Princeton University
> ----------------------------------------------------------------------
>
> Ch3 Sec2.3.14. ATAN2
>
> Current documentation (3/20/01)
> http://ferret.wrc.noaa.gov/Ferret/Documentation/Users_Guide/v52/Chapter3.htm#_VPINDEXENTRY_203
> -------------------------------
> ATAN2(X,Y)  2-argument trigonometric arctangent of Y/X (-pi,pi);
> discontinuous at Y=0.  ATAN2( X,Y ) computes the 2-argument arctangent
> of Y/X for all points within the current region
>
> [According to this, would have ATAN2(0,1)==pi/2, ATAN2(1,0)==0,
> which is not what Ferret actually does.]
>
> Ferret v5.22 program
> --------------------
> yes? list atan2(0,1)
>              ATAN2(0,1)
>           0.0000
> yes? list atan2(1,0)
>              ATAN2(1,0)
>           1.571
>
> Proposed new documentation
> --------------------------
> ATAN2(Y,X)  2-argument trigonometric arctangent of Y/X (-pi,pi);
> discontinuous at Y=0.  ATAN2( Y,X ) computes the 2-argument arctangent
> of Y/X for all points within the current region

--
Ansley Manke  Pacific Marine Environmental Laboratory  Seattle WA  (206)526-6246