Re: Motion 52: final "Expressions" text for vote
On 2013-11-22 16:18:13 +0100, J. Wolff von Gudenberg wrote:
> Vincent
> Am 22.11.2013 13:19, schrieb Vincent Lefevre:
[...]
> >I have some questions:
> I propose some answers:
[...]
I would have liked you to quote the current standard text to makes
clear that everything is correctly specified.
> >1. Is the above sentence of §8.2 an error or does the standard
> >require this to be still true for NaI? In any flavor?
> NaI propagates in all operations, but NaI is NotanInterval
Until now it was considered to be (Empty,ill), which has an interval
part, thus is an interval. Something needs to be fixed.
> >3. In the set-based flavor, according to the propagation order, if
> >there's a NaI in input (thus will decoration ill), then the result
> >shall have the decoration ill. Does the standard require that such
> >an interval be Empty?
> the decoration ill is only used by NaI. intervalPart(naI) is
> undefined and causes an exception
> >
> >§11.4 doesn't seem to forbid NonEmpty_ill: it doesn't mention ill
> >at all and says "No other combinations are essentially forbidden."
> >but perhaps the ill case has been forgotten.
> IMO ill is not a decoration, it only goes with NaI
See the definitions:
4.2.12. decoration. One of the flavor-defined sets of values used to
record events, called exceptional conditions, in interval operations:
e.g., evaluating a function at points where it is undefined. The
set-based flavor uses the five values com, dac, def, trv and ill,
^^^
see Clause 11.
I can see 2 solutions:
1. Remove the ill decoration and make NaI a special datum, not regarded
as a (decorated) interval. But everything about ill in the text should
be corrected. One advantage is that this would make NaI handling simpler
and flavor-independent. A drawback is that one would have a special
object.
2. Keep "decorated interval" = (interval,decoration) pair, possibly
with forbidden combinations. Then one thing to think about is: should
the equivalence
bare evaluation == interval_part(decorated evaluation)
be kept too?
> >4. In the set-based flavor (and other flavors supporting Empty?),
> >in the bare version, if there is an Empty in input (thus the box
> >is empty), shall the result be Empty?
> yes
Where is it specified?
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)