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Re: max() and min() of nan/inf
From: |
Olli Saarela |
Subject: |
Re: max() and min() of nan/inf |
Date: |
Tue, 21 Sep 1999 09:00:32 +0300 |
Hello,
> Is this a correct behaviour?
>
> max() or min() return nan is a nan is one of its arguments? max() or
> min() considering +/-Inf looks OK.
Yes, it is correct. Of course this is a matter of definition (defined in
the IEEE Standard 754), but the following example tries to give some
rationale:
John is 186 cm long.
Mark is 176 cm long.
I don't know how long Philip is (= NaN).
How long is the longest of them (= max)? Can't be answered (= NaN).
A NaN value (Not a Number) is not a real number. It doesn't have a
magnitude which could be compared. The min and max functions return the
smallest and the largest number of the set of numbers given. When the
set contains a NaN, the numbers don't any more have a minimum or a
maximum value. Hence, the value NaN is returned, indicating that there
is no number equal to the minimum or maximum value of the set.
> arithmetic or comparition operations
> are of course not defined on nans...
But they are defined. Any arithmethic operation with a NaN operand is
defined to evaluate to NaN. Any comparison with a NaN operand is defined
to evaluate to FALSE (except the ~= operation to TRUE).
For example:
Is NaN bigger than 3? No. (NaN > 3) --> FALSE
Is NaN smaller than 3? No. (NaN < 3) --> FALSE
Is NaN equal to 3? No. (NaN == 3) --> FALSE
For more complete description, please see:
http://www.lpthe.jussieu.fr/DOC_HTML/WorkShop/common-tools/numerical_comp_guide/goldberg1.ps
Best regards,
Olli
--
Olli Saarela KCL Development Oy
address@hidden tel. +358-9-4371538 (office)
Tekniikantie 2, Espoo-Otaniemi fax. +358-9-464305
P.O. Box 70, FIN-02151 Espoo, Finland
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- max() and min() of nan/inf, Joao Cardoso, 1999/09/16
- Re: max() and min() of nan/inf,
Olli Saarela <=
- Re: max() and min() of nan/inf, Joao Cardoso, 1999/09/22
- Re: max() and min() of nan/inf, Olli Saarela, 1999/09/23
- Re: max() and min() of nan/inf, Mirek Kwasniak, 1999/09/23
- Re: max() and min() of nan/inf, Mike Miller, 1999/09/23
- Re: max() and min() of nan/inf, John W. Eaton, 1999/09/23
- Re: max() and min() of nan/inf, Thomas Walter, 1999/09/24
- Re: max() and min() of nan/inf, Joao Cardoso, 1999/09/23
- Re: max() and min() of nan/inf, Jonathan King, 1999/09/23