Re: Past uses of NaN?
On 2010-11-02 14:01:55 +0100, Arnold Neumaier wrote:
> To check that we forget nothing of relevance, it would be useful if
> someone could collect the main different uses (or suggested uses)
> that NaNs have in past applications. At present, I am aware of
> three different systematic uses, the first two corresponding to
> the above two cases:
>
> -- signalling ''invalid''; e.g., sqrt(-1)=NaN;
> -- signalling ''arbitrary''; e.g., 0/0=NaN; inf-inf=NaN;
> -- signalling ''missing value''; e.g., max(1,NaN,4,2)=4.
I think that 0/0 and sqrt(-1) can fall under the same category.
0/0 is mathematically invalid, but can occur in practice due to
rounding errors. Ditto for sqrt(-1).
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Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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