On 3/22/2006 3:52 AM, [EMAIL PROTECTED] wrote: >>>>>> "cspark" == cspark <[EMAIL PROTECTED]> >>>>>> on Wed, 22 Mar 2006 05:52:13 +0100 (CET) writes: > > cspark> Full_Name: Chanseok Park Version: R 2.2.1 OS: RedHat > cspark> EL4 Submission from: (NULL) (130.127.112.89) > > > > cspark> pbinom(any negative value, size, prob) should be > cspark> zero. But I got the following results. I mean, if > cspark> a negative value is close to zero, then pbinom() > cspark> calculate pbinom(0, size, prob). > > >> pbinom( -2.220446e-22, 3,.1) > [1] 0.729 > >> pbinom( -2.220446e-8, 3,.1) > [1] 0.729 > >> pbinom( -2.220446e-7, 3,.1) > [1] 0 > > Yes, all the [dp]* functions which are discrete with mass on the > integers only, do *round* their 'x' to integers. > > I could well argue that the current behavior is *not* a bug, > since we do treat "x close to integer" as integer, and hence > pbinom(eps, size, prob) with eps "very close to 0" should give > pbinom(0, size, prob) > as it now does. > > However, for esthetical reasons, > I agree that we should test for "< 0" first (and give 0 then) and only > round otherwise. I'll change this for R-devel (i.e. R 2.3.0 in > about a month). > > cspark> dbinom() also behaves similarly. > > yes, similarly, but differently. > I have changed it (for R-devel) as well, to behave the same as > others d*() , e.g., dpois(), dnbinom() do.
Martin, your description makes it sound as though dbinom(0.3, size, prob) would give the same answer as dbinom(0, size, prob), whereas it actually gives 0 with a warning, as documented in ?dbinom. The d* functions only round near-integers to integers, where it looks as though near means within 1E-7. The p* functions round near integers to integers, and truncate others to the integer below. I suppose the reason for this behaviour is to protect against rounding error giving nonsense results; I'm not sure that's a great idea, but if we do it, should we really be handling 0 differently? Duncan Murdoch ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
