Thanks a lot - it's been helpful. Look like it has to be pretty darn close to zero to be considered = 0. D.
On Fri, Mar 26, 2010 at 3:22 AM, Prof Brian Ripley <rip...@stats.ox.ac.uk> wrote: > On Fri, 26 Mar 2010, Rolf Turner wrote: > >> >> On 26/03/2010, at 12:38 PM, jim holtman wrote: >> >>> WHen using '==' or '%in%' it is a equality test -- it has to equal zero. >>> If >>> you want a tolerance in the test, use 'all.equal' >>> >>> On Thu, Mar 25, 2010 at 5:29 PM, Dimitri Liakhovitski >>> <ld7...@gmail.com>wrote: >>> >>>> Hello! >>>> >>>> I am wondering at what point does R consider a numeric value to be >>>> equal to zero - for statements of the type x==0 and x %in% 0. >>>> >>>> Thank you very much! >> >> >> There is still perhaps a question to be answered here. One can key in >> a representation of a number, different from ``0'' and yet get a value >> deemed to be 0 by the machine. >> >> E.g. on my machine >>> >>> 1e-324 == 0 >> >> [1] TRUE >>> >>> 1e-323 == 0 >> >> [1] FALSE >> >> The question of where the line is drawn is probably ill-posed or >> meaningless >> or something like that. It's not clear to me what the issues are. Also >> the >> answer, if there is a meaningful one, is likely to be machine dependent >> rather >> than R dependent. > > Nope, for OSes whose runtimes use the IEC 60559 standard (almost all of > them, as these functions are mainly done in the FPU). > > The smallest normalized non-zero double is > >> .Machine$double.xmin > > [1] 2.225074e-308 > > For numbers smaller than that there is gradual overflow to zero via > denormalized numbers. > > The general principle is that when a number if parsed, the closest > representable double is used: and for "1e-324" that is zero. > >> >> cheers, >> >> Rolf Turner > > > -- > Brian D. Ripley, rip...@stats.ox.ac.uk > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 > > ______________________________________________ > 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. > -- Dimitri Liakhovitski Ninah.com dimitri.liakhovit...@ninah.com ______________________________________________ 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.