Stavros Macrakis wrote: > On Sat, Dec 6, 2008 at 5:02 AM, Wacek Kusnierczyk < > [EMAIL PROTECTED]> wrote: > > >> yepp, though (2/3)*3 not evaluating to 2 is again not a must, is it. >> > > > Why is that less a must than .3-.2 == .1? On the contrary, the computing > convention (and for that matter the usual scientific and engineering > convention) is that a decimal point signals an approximate number. >
not a must, since no floating point arithmetic has to be involved here. > > >> you know scheme would say (* (/ 2 3) 3) is 2 >> > > > Yes, Scheme uses rational arithmetic. > > > >> , and similarly for (* (/ 2.0 3.0) 3.0) >> > > > Yes, Scheme uses standard (correctly rounded) IEEE floating point, but of > course other cases like 15.0/22.0*22.0 are not exact. > (* (/ 2.0 3.0) 3.0) is not exact either, as aren't (* (/ 2.0 2.0) 2.0) and 2.0; this was a teaser ;) > > >> ...it's all about representations, but representations are typically below >> the interface. i did not complain, or troll, about r not implementing >> arbitrary precision, just remarked that the example and its explanation >> expose a user to the internals. >> > > > No, I don't think that's the correct way to think about it. I believe that > the R spec says (or should say) that "numeric" means IEEE double-precision > floats, with all that that entails: range restrictions, precision, rounding > rules, NaNs, etc. > maybe. > > >> ...original question about 8.8-7.8 not being 1. the result is finely >> explained by reference to the underlying representation, but this does break >> the assumption of isolation from underlying details, claimed here once upon >> a time. >> >> > > Sounds like a pretty naive claim for a language which after all doesn't even > have a formal definition (besides the implementation). Not that formal > definitions are a panacea -- having been a "language lawyer" in a compiler > group many years ago, I can attest that they are not (but that is a > different, long discussion). > to be fair to the referred to post, it went: "One of the key design features of R is that it hides implementation details from users. They are free to think about the substantive issues with their data rather than worrying about computational trivia." vQ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.