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Re: Alternate floating-point results under directed rounding

On Fri, 07 Nov 2008 11:17:59 -0100, Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx> wrote:

I don't understand.
 To have 0*[1,inf] = [0,0], no interpretation of inf as floating-point
is needed, since this automatically holds with the specification of
    [l,u] = set of reals between l and u.
No conversion of inf to an interval is involved here.

Consider (in Matlab notation)

   X = intval(NaN);
   Y = 0*X

The result is the empty set, in either way. We expect this.

   X = intval(0.1);
   Y = 0*X

The result is [0], in either way. We expect this.

   X = intval(1e40);
   Y = 0*X

The result is still [0], either way. We expect this.

   X = intval(1e400);
   Y = 0*X

Your result is the empty set. Strange? I think yes.

As you say, we can define everything as we wish.
I prefer a definition so that Y is still [0].

Cheers,  Siegfried

Prof. Dr. Siegfried M. Rump
Institute for Reliable Computing
Hamburg University of Technology
Schwarzenbergstr. 95
21071 Hamburg
phone  +49 40 42878 3027
fax    +49 40 42878 2489


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