On Sat, Dec 6, 2008 at 4:32 PM, Wacek Kusnierczyk < [EMAIL PROTECTED]> wrote:
> 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. > Floating-point is not the issue here. Fixed point is just as bad. The problem is that it is a binary fraction, not a decimal fraction. It is perfectly possible to do decimal arithmetic in computers, and it is useful for commerical, but not scientific/engineering calculations. > 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 ;) > Actually, they *are* all exact in any system using IEEE floats. > 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. > Some other language systems have tried other approaches to specifying float accuracy. For example, the original Ada spec had its own floating-point error model, which allowed a greater range of results to be considered "correct". > > Sounds like a pretty naive claim... > > 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." > This is just puffery: *"Puffery* as a legal term<http://en.wikipedia.org/wiki/Legal_term>refers to promotional statements <http://en.wikipedia.org/wiki/Advertising> and claims that express subjective <http://en.wikipedia.org/wiki/Subjectivity> rather than objective <http://en.wikipedia.org/wiki/Objectivity_%28journalism%29> views, such that no reasonable person would take literally." (Wikipedia) Every language claims that it is a better level of abstraction for users' problems and hides the "computational trivia" from the user. R certainly abstracts from a lot of "computational trivia" that you'd have to deal with in Fortran or C, but in the end you can't take these things too literally. -s [[alternative HTML version deleted]] ______________________________________________ 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.
