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Re: min / max and empty intervals - Entire and Missing Data



On 2011-06-13 22:59:32 +0100, John Pryce wrote:
> All
> 
> On 10 Jun 2011, at 11:02, Dominique Lohez wrote:
> > A important point which must be noticed
> > 
> > John is defining NaN
> >                                as a   LEVEL 1   CONCEPT
> 
> Let me clarify. At level 1, NaN is not a *value* that can be taken
> by a real variable, or can be returned by a real function. I'm
> following the standard mathematical formalism that for a real
> function f of n real variables, and x in R^n, f(x) either is
> "defined" and is a real number (if x in D_f) or is "undefined". An
> alternative scheme could be used, namely to say f(x) has some value
> NaN if x not in D_f, but that is a different formalism.

This shouldn't be called "NaN" then (this term can lead to confusion
and has several meanings, e.g. a defined but unknown value). You can
call it Undef or Bottom.

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Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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