Re: pred & succ ?

[Martin Schultz <martin.schultz(at)dkrz.de>]

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


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