Umm, Raul, I've had a glance at some of the documentation and I'm not sure you're right here. Check out:
http://arith22.gforge.inria.fr/slides/06-gustafson.pdf The bit on "The Wrath of Kahan" struck me as fairly convincing. My 2c, Jo. On 28 April 2016 at 16:58, Raul Miller <[email protected]> wrote: > When I run through my head examples of how that would work in > algorithms I have worked on, it seems to me that it (a) it starts out > with less precision than floating point (because of the extra bits > being used for representing an estimate of accuracy), and (b) that it > would tend to also lose precision faster (because it started out with > less, so the fractional bits being lost are more significant). > > Put differently: as long as (a) this representation stays close to > original data, and (b) the people using it understand in detail how it > works, it will probably be ok. But run this through a lengthy sequence > of calculations and it'll mess up faster than floating point. > > Put differently: I prefer J's approach of providing ":!.precision (or > 9!:11) over these things. > > That said, running through the calculation once using unums (to get a > precision estimate) and then running through it again using floating > point (to get a more precise result) might be a useful approach (for > applications where the factor of 2 time and space cost is acceptable). > > That said, it is fun reading about how other people think about these > things. > > Then again, there presumably must be applications where unums are a > better fit than floating point? (I just don't know much about what > those might be, off the top of my head.) > > -- > Raul > > > > On Wed, Apr 27, 2016 at 11:36 PM, 'Jon Hough' via Chat > <[email protected]> wrote: > > This interview is pretty interesting, about a new number format that > will solve floating point related errors: > > http://ubiquity.acm.org/article.cfm?id=2913029 > > > > see also: > http://motherboard.vice.com/read/a-new-number-format-for-computers-could-nuke-approximation-errors-for-good > > > > I wonder about a J implementation of unums... ...it seems Julia (among > others) has one > > https://github.com/REX-Computing/unumjl > > > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
