| 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 [[
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