| Re: ATAN function with two ARGS [message #20279] |
Tue, 06 June 2000 00:00 |
K. Bowman
Messages: 330
Registered: May 2000
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Senior Member |
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In article <MPG.13a582048e3c14e9989b49@news.frii.com>, David Fanning
<davidf@dfanning.com> wrote:
> Ben Tupper (tupper@seadas.bigelow.org) writes:
>
>> 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.
>
> Notice they don't say the "result of the function" is
> undefined. If they did, I could understand your confusion.
> But here they have made a truthful and accurate statement.
> *Implying* that they were talking about the result of the
> function is an old technical writers trick that allows one
> to remain truthful, while still confusing the rift-raft.
The result of ATAN(0.0,0.0) in IDL is implementation dependent, viz.
Logging into SGI IRIX
IDL Version 5.3 (IRIX mipseb). (c) 1999, Research Systems, Inc.
IDL> print, atan(0.0, 0.0)
0.00000
Logging into DEC Unix
IDL Version 5.3 (OSF alpha). (c) 1999, Research Systems, Inc.
IDL> print, atan(0.0, 0.0)
-NaN
In some cases it really is undefined. ;-)
Ken
One of the riff-raff (i.e., those people or that segment of society
regarded as worthless, disreputable, insignificant, etc.; rabble)
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| Re: ATAN function with two ARGS [message #20280 is a reply to message #20279] |
Tue, 06 June 2000 00:00  |
Ben Tupper
Messages: 186
Registered: August 1999
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Senior Member |
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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
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| Re: ATAN function with two ARGS [message #20285 is a reply to message #20279] |
Mon, 05 June 2000 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Ben Tupper (tupper@seadas.bigelow.org) writes:
>> From now on I'm writing
>> with a renewed spirit of obfiscation. Where's my thesarus?!
>>
>
> I'm off to a great start! Obfuscate!
Oh, shoot. And I thought you were trying to
get points with the IDL EPA nominating committee
for "unintentional humorous composition." :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: ATAN function with two ARGS [message #20287 is a reply to message #20285] |
Mon, 05 June 2000 00:00 |
Ben Tupper
Messages: 186
Registered: August 1999
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Senior Member |
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David Fanning wrote:
> Ben Tupper (tupper@seadas.bigelow.org) writes:
>
>> 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.
>
> Notice they don't say the "result of the function" is
> undefined. If they did, I could understand your confusion.
> But here they have made a truthful and accurate statement.
> *Implying* that they were talking about the result of the
> function is an old technical writers trick that allows one
> to remain truthful, while still confusing the rift-raft.
>
> You have to read this documentation *much* more carefully,
> Ben, if you have any hopes of winning a commission
> in the IDL Expert Programmers Association. :-)
>
Geez,
I am beginning to suspect that entry into IDL EPA requires much more
subtle documentation than I have been writing. From now on I'm writing
with a renewed spirit of obfiscation. Where's my thesarus?!
You don't suppose that Oscar Gamble wrote the documentation do you?
Ben
--
Ben Tupper
Bigelow Laboratory for Ocean Science
tupper@seadas.bigelow.org
pemaquidriver@tidewater.net
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| Re: ATAN function with two ARGS [message #20288 is a reply to message #20285] |
Mon, 05 June 2000 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Ben Tupper (tupper@seadas.bigelow.org) writes:
> 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.
Notice they don't say the "result of the function" is
undefined. If they did, I could understand your confusion.
But here they have made a truthful and accurate statement.
*Implying* that they were talking about the result of the
function is an old technical writers trick that allows one
to remain truthful, while still confusing the rift-raft.
You have to read this documentation *much* more carefully,
Ben, if you have any hopes of winning a commission
in the IDL Expert Programmers Association. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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