Re: Fwd: The definition of cancel_minus
On 2016-09-19 09:43:38 -0300, Walter Mascarenhas wrote:
> Dear colleagues,
>
> I am implementing the function cancel_minus
> and I do not understand the rational behind
> its definition in the standard. In the "normal case"
> (ie. non empty and bounded intervals) section
> 10.5.6 of the standard states that
>
> Definition I: cancel_minus(sum, parcel) = tightest interval c
> such that parcel + c contains sum.
>
> In my opinion, the definition should be
>
> Definition II: cancel_minus(sum, parcel) =
> (the convex hull of) the union of all intervals c
> such that parcel + c is contained in sum.
IIRC, I was wondering something like that, said otherwise:
* At Level 1, one wants to have: parcel + c = sum.
* At Level 2, one normally rounds outwards. But here, since this
is a reverse operation, I was wondering whether one should round
inwards (which should probably be specified as your Definition II).
But as I am not a user of this function, I didn't think further
about it. So, I understand your point, but I don't have any
opinion on the subject concerning what users expect.
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <https://www.vinc17.net/>
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