Re: ATAN function with two ARGS

[Ben Tupper <tupper(at)seadas.bigelow.org>]

Ben Tupper wrote:

> In comp.lang.idl-pvwave you write:
>
> >Hello,
>
> >I have bumped into a conflict between the IDL documentation and IDL output.
>
> >From the IDL (5.2) docs, the optional argument Y is described as follows:
>
> >-------START
> >Y
> >An optional argument.
>
> >If this argument is supplied, ATAN returns the angle whose tangent
>
> >is equal to Y/X. If both arguments are zero, the result is undefined.
>
> >------END
>
> >So I tried the following...
>
> >IDL> help, ATAN(0.0,0.0)
> ><Expression>    FLOAT     =       0.00000
>
> >Uhoh! Is it me, or is it Monday morning syndrome?
>
> >Ben
>
> When I try the above command, I get
>
> IDL> help,atan(0.0,0.0)
> <Expression>    FLOAT     =          -NaN
>
> IDL> help,/struct,!version
> ** Structure !VERSION, 5 tags, length=80:
>    ARCH            STRING    'alpha'
>    OS              STRING    'OSF'
>    OS_FAMILY       STRING    'unix'
>    RELEASE         STRING    '5.2'
>    BUILD_DATE      STRING    'Oct 30 1998'
>
> William Thompson
>

The above was sent to me by  William Thompson.   Below is the version info for
the platform not returning the undefined value.
I've sent notice of this anomaly to RSI.

Thanks,

Ben

IDL> help,!version
<Expression>    STRUCT    = -> !VERSION Array[1]
IDL> help,!version,/str
** Structure !VERSION, 5 tags, length=40:
   ARCH            STRING    'sparc'
   OS              STRING    'sunos'
   OS_FAMILY       STRING    'unix'
   RELEASE         STRING    '5.2'
   BUILD_DATE      STRING    'Oct 30 1998'
IDL> help, ATAN(0.0, 0.0)
<Expression>    FLOAT     =       0.00000


--
Ben Tupper

Bigelow Laboratory for Ocean Science
tupper@seadas.bigelow.org

pemaquidriver@tidewater.net