Re: Motion P1788/M007.01_NaI: Discussion period begins
On 2009-08-05 13:37:37 -0400, Ralph Baker Kearfott wrote:
> Since Motion 7 has been made by Juergen Wolff von Gudenberg and
> seconded by Rudnei Cuhna, the discussion period now begins, and
> will end after Wednesday, August 28. I append Juergen's
> motion and attachment.
Some comments:
2.1 says: "According to motion 3, if both arguments are finite numbers
and l ≤ u, or l equals −∞, or u equals +∞ that constructor returns the
F interval [l,u] otherwise NaI is returned."
You should also exclude the cases l = u = −∞ and l = u = +∞.
"Since there are many possible encodings of NaN, NaI and the empty set
both can be represented as different pairs of NaNs, NaI as [-NaN,-NaN],
the empty set as [+NaN,+NaN], e.g."
Testing the sign bit of a NaN may not be optimal. I'd rather say:
Empty set: [NaN,NaN]
NaI: [NaN,non-NaN]
and any other implemention-defined encoding (e.g. if NaN is not
supported by the underlying arithmetic).
2.2 Arguments
Another argument against NaI: there are different and contradictory
NaI concepts. For instance, if NaI is used for missing data, then
min(some_interval,NaI) should return some_interval, not NaI.
"There is an obvious analogy to 754 NaN"
Very partially. NaN can also mean [−∞,+∞] (any real number), as in
hypot(+∞,qNaN), or also the empty set (e.g. result of sqrt(-1)).
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)