You might use the idea below together with sum.exact in the caTools package.
On 11/17/06, Martin Maechler <[EMAIL PROTECTED]> wrote: > >>>>> "Paul" == Paul Smith <[EMAIL PROTECTED]> > >>>>> on Fri, 17 Nov 2006 12:12:52 +0000 writes: > > Paul> On 11/16/06, Prof Brian Ripley <[EMAIL PROTECTED]> > Paul> wrote: > >> > For my calculations, I am needing to use more > >> floating-point precision > than the default one of R. Is > >> that possible? And, if yes, how? > >> > >> See package gmp (but that will be slow and cumbersome for > >> all but simple calculations). > >> > >> The real issue is that R already uses the maximum > >> precision of the FPU for many common FPUs (but not all). > >> Since you have forgotten to tell us anything about your > >> environment we don't know if that applies: there may be > >> compiler options you can use to raise the precision. > >> > >> Please do study the posting guide: we are surprisingly > >> good at mind-reading, but prefer to be told exactly what > >> you want to do with R in what environment and why you are > >> 'needing' something. > > Paul> Thanks, Gabor and Prof. Ripley. After some research, I > Paul> conclude that the problem occurring to me cannot be > Paul> removed for any finite floating-point precision. (I do > Paul> need infinite floating-point precision.) The > Paul> problematic operation is the successive multiplication > Paul> of reals between 0 and 1; after a certain number of > Paul> multiplications, significant rounding errors occur. > > of course. But that's a very well known and common problem in > several areas of applied probability and statistics. > > AFAIK, in most cases the "obvious" remedy is the following: > Instead of multiplying probabilities, > you add log-probabilities and only exp()onentiate at the end {if > needed at all}. This also applies if your numbers in [0,1] are > not probabilities per se. > > Note that R makes it particularly efficient to work with > log-probabilities, because all d<foo>() and p<foo> functions > have a 'log' or 'log.p' argument which return log-values > already, often with much more precision and efficiency than if > you'd take the log of the probabilities yourself. > > Regards, > Martin Maechler, ETH Zurich > > > Paul> I did read the posting guide, but I could not > Paul> anticipate the relevance of indicating the environment > Paul> that I am using: Fedora Core 6 (Linux) running on a > Paul> Pentium Dual Core and R 2.4.0. > > Paul> Paul > > Paul> ______________________________________________ > Paul> R-help@stat.math.ethz.ch mailing list > Paul> https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do > Paul> read the posting guide > Paul> http://www.R-project.org/posting-guide.html and > Paul> provide commented, minimal, self-contained, > Paul> reproducible code. > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > ______________________________________________ R-help@stat.math.ethz.ch 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.