| Re: pred & succ ? [message #22450] |
Mon, 13 November 2000 00:00 |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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Andrew wrote:
>
> In article <3A0FA91A.7BEE1D07@dkrz.de>,
> Martin Schultz <martin.schultz@dkrz.de> wrote:
>>
>> FUNCTION pred, x
>> RETURN, x-1
>> END
>> FUNCTION succ, x
>> RETURN, x+1
>> END
>>
>
> Thanks, Martin. I take that as a "no", though.
>
> I was thinking of a general, built-in (thus fast),
> function that returns the successor or predecessor
> of any ordinal variable.
>
> I knew I could write x-1, etc.. :-)
>
Well, the point is that x-1 already is quite fast because IDL is array
oriented. I'm not sure whether you could gain anything significant by
having this as a builtin function.
Cheers,
Martin
--
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
[[ Dr. Martin Schultz Max-Planck-Institut fuer Meteorologie [[
[[ Bundesstr. 55, 20146 Hamburg [[
[[ phone: +49 40 41173-308 [[
[[ fax: +49 40 41173-298 [[
[[ martin.schultz@dkrz.de [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
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| Re: pred & succ ? [message #22455 is a reply to message #22450] |
Mon, 13 November 2000 00:00  |
noymer
Messages: 65
Registered: June 1999
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Member |
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In article <3A0FA91A.7BEE1D07@dkrz.de>,
Martin Schultz <martin.schultz@dkrz.de> wrote:
>
> FUNCTION pred, x
> RETURN, x-1
> END
> FUNCTION succ, x
> RETURN, x+1
> END
>
Thanks, Martin. I take that as a "no", though.
I was thinking of a general, built-in (thus fast),
function that returns the successor or predecessor
of any ordinal variable.
I knew I could write x-1, etc.. :-)
-- Andrew
Sent via Deja.com http://www.deja.com/
Before you buy.
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| Re: pred & succ ? [message #22457 is a reply to message #22450] |
Mon, 13 November 2000 00:00 |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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Andrew wrote:
>
> Dear C.l.i-p,
>
> In Pascal (and probably in other high-level languages,
> but I don't know), there are built-in functions PRED(x)
> & SUCC(x), where x is any ordinal-type variable.
>
> e.g.: PRED(1)=0
> SUCC(2)=3
> PRED(TRUE)=FALSE
>
> etc., etc.
>
> Is there anything like this in IDL?
>
> -- Andrew
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
FUNCTION pred, x
RETURN, x-1
END
FUNCTION succ, x
RETURN, x+1
END
But is that really worth it? You won't be able to construct
pred(false) for there is no distinct "false" in IDL. But this is
actually a nice little "Denksportaufgabe" (although I am sure you can
find a solution on some webpage, too): How do you construct a reliable
complement of a variable that represents a boolean?
Hints:
- should accept any (numerical) type (ok, maybe not complex ;-)
- variable type should be preserved
- 0 is false, everything else true (how about 1.e-30? - probably best
to define an "eps"); in output, "true" should be 1
- should not be constrained to scalars (IF(...) won't work)
Thanks to RSI for not providing us with a dedicated "logical" or
"boolean" type. Otherwise this would be too trivial ;-)
Cheers,
Martin
--
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
[[ Dr. Martin Schultz Max-Planck-Institut fuer Meteorologie [[
[[ Bundesstr. 55, 20146 Hamburg [[
[[ phone: +49 40 41173-308 [[
[[ fax: +49 40 41173-298 [[
[[ martin.schultz@dkrz.de [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
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