Re: Motion P1788/M0032.01:MidpointMeaning -- discussion period begins
On 2012-04-05 15:23:06 +0100, John Pryce wrote:
> That's why I explicitly say in my draft Level 2 text that such an
> interpretation of "variable-precision" is incompatible with P1788.
> To conform with IEEE 1788, a VP interval system must interface in
> such a way that at any moment it is working with intervals of a
> given precision. I.e., it supports a potentially infinite family of
> interval types T_d, parameterized by some measure d of the number of
> digits of precision. Not a single type that is the union of these.
>
> I suspect this will be unpopular with the authors of some VP
> systems, but it is a simple way to cut that Gordian knot; in fact
> the only way that I can see at present.
I don't think there would be any problem with MPFR-based IA systems,
because with MPFR, the user must specify the precision of the result
(e.g. this is done when initializing the target object or by changing
its precision). So, basically, the user specifies the parameterized
type. It could be a problem with systems that dynamically chooses the
precision of the result (e.g. from the internal error bound, which
is calculated dynamically); but I think that it should be OK, except
that the notion of "tightest" (and "accurate"?) will no longer be
usable.
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)