Berwin A Turlach wrote: > G'day Wacek, > g'evening.
> On Sat, 06 Dec 2008 10:49:24 +0100 > Wacek Kusnierczyk <[EMAIL PROTECTED]> wrote: > > [....] > >>>> there is, in principle, no problem in having a high-level language >>>> perform the computation in a logically consistent way. >>>> >>> Is this now supposed to be a "Radio Eriwan" joke? As another saying >>> goes: in theory there is no difference between theory and practice, >>> in practice there is. >>> >> no joke, sorry to disappoint you. >> > > Apparently it is, you seem to be a comedian without knowing it. :) > > "Radio Eriwan" jokes are a class of jokes in which a question was posed > to the announcer of "Radio Eriwan", a fictive radio station. The > answer was always "In principle yes, but..." or "In principle no, > but..."; the part that came after the but contradicted the initial > answer. If you know a little bit of German, google for "Radio Eriwan" > and you will find out more about these jokes. > > c'mon, a person from central europe can't possibly be unaware of this joke. i know of a 60-page book collecting radio erewan jokes. deadly serious. > So your posting would be a classical "Radio Eriwan" answer to a yet > to specify question: "In principle, no problem of having a > high-level language perform the computation in a logcally consistent > way, but [...] i do not claim that r should implement arbitrary > precision floating point arithmetic [and] if you have involving > computations on floats it would make little sense to implement > arbitrary precision." > > Classical Radio Eriwan stuff, and I thought this class of jokes have > died out..... > apparently not, as long as there are people able to find them in whatever they read. > >> [...] the point was, the user was surprised, and the answer pointed >> her, if indirectly, to an article which is addressed to computer >> scientists and discusses low-level representational details, but the >> user was presumably interested in stats, not computer science. so >> the answer felt like lacking a justification. >> > > First, I think it is a rather ambitious jump in logic that a user is > interested in stats because the user wants to see whether "8.3 - 7.3 > > 1" is true. The only indication of the user being interested in > stats would be that the user used R, which is used primarily for > statistical analysis; that was my reasoning, good god! > though some people apparently use it also as a > scripting language instead of Perl or Python. oh my. > If the user had typed > this into matlab/octave/scilab/YouNameIt, would would you have thought > that the user is interested in? > > Secondly, that the FAQ points to an article that is addressed to > computer scientists is coincidental and not really of any importance. > There is a Wiley & Sons book called "Numerical Issues in Statistical > Computing for the Social Scientist", plenty of books on numerical > analysis, plenty of books for numerical analysis or numerical linear > algebra for statisticians that discuss issues that arise when you start > to do calculations in finite precision arithmetic. You could probably > write papers entitled "What Every XXXX Scientist Should Know About > Floating-Point Arithmetic" for every possible XXXX. It just so happens > that the article by Goldberg is one that is freely available on the > internet and it is much better to point people to this article than to > any of the myriads of books that exist on this topic but which they > would first have to get from the library. > > If you know of any other freely available article that discusses these > issues, and that you think is more appropriate for pointing useRs to, > feel free to suggest to the FAQ maintainers to change the citation. > > unfortunately, i only have quite a couple of books on the subject, none of which is freely available. at least, not in a way their publishers would gladly accept. i'd agree that it's not a drawback to know how arithmetic is actually done on computers (but hey, there is no unique standard here). but many people i know (which certainly makes a poor statistic) would prefer to be abstracted away from having to know that 8.8-7.8 > 1 is true, less so why it is true. >>> But you are wrong here, R performs logically *in the logic of finite >>> precision arithmetic*. The problem is that you are using finite >>> precision arithmetic but expect that the rules and logic of infinite >>> precision arithmetic hold. If you want to use have infinite >>> precision arithmetic, then use a tool that (supposedly) implements >>> it. >>> >> well, it clearly depends what you regard as logical. you can have r >> say '1==0' is true, and argue that it's correct by the logic adopted. >> > > Either infinite precision arithmetic or finite precision arithmetic, in > neither of this would "1==0" being true be logical. > not difficult at all to define an arithmetic where 1==0 is true, document it in a man page, and refer to it when complaints come. surely, an exotic example. > Though, I once read that Kahan managed to get Mathematica to believe > that 1==0. It must have been some time ago, so probably was an old > version of Mathematica. Kahan started with two expressions that were > logically, in infinite precision arithmetic, identical, so Mathematica > agreed that they were the same. But when then asked to evaluate both > expression numerically, Mathematica evaluated one expression to 1 and > the other to 0 and, thus, started to believe that 1==0. > > >> fine. the issue is, if you assume your users are statisticians, not >> computer scientists, you should not be surprised the logic some of >> them assume differs from the one you implement. >> > > If I assume that my users are statisticians, then I would assume that > they have learned during their training about finite precision > arithmetic and know about these problems. Though, they might have > forgotten about having learned about it.. i know of cs guys who either have forgotten, or have never learned (!). assuming familiarity with these representational-computational issues among statisticians seems a bit too strong to me, but i am not a statistician myself, so it's easy to misjudge. you say. 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.
