Re: Motion P1788/M0032.02: I vote NO
Vincent Lefèvre a écrit:
> On 2012-04-15 23:49:20 -0400, Michel Hack wrote:
> > I vote NO on M0032.02 -- the main issue for me being that the Level 2
> > midpoint might not be a member,
>
> a member of what?
A member of the interval whose "midpoint" is being taken. This can
happen for certain off-center "implicit" formats.
> > so the mention of Ýinf_F(X),mid_F(X)¨ might be meaningless.
>
> Could you give an example? AFAIK, Ýinf(X),mid_F(X)¨ can be meaningless,
> but Ýinf_F(X),mid_F(X)¨ is a valid interval, as pointed out by Dmitry
> in a recent discussion.
Ah yes, that subtlety had escaped me! I apologise. To some extent this
means that my objections become more an issue of comfort than substance.
It does however require including Dmitry's (who btw signs "Dima" -- in
Russian (and Spanish too) colloquial first names often look quite different
from corresponding formal names) definition of inf_F and sup_F based on
the hull_t() function required of implicit types. Motion 19 on implicit
types did not define inf_F and sup_F (because the concept of _F had not
yet been exposed).
So I would vote YES if the definitions of inf_F and sup_F were included,
still being uncomfortable however about reporting a "midpoint" that is
outside the interval (as I said, I would prefer NaN in this case).
Another issue bothered me slightly: the use of round2Nearest(Level1mid).
I wonder if thered might be cases where this rounding yields an exterior
point, whereas rounding in the other direction (by more than half an ulp)
would yield an interior point. Upon reflection however this cannot
happen for bounded intervals, so I don't have to worry about this.
Michel.
---Sent: 2012-04-16 16:07:41 UTC