A point of clarification: dDIST() sometimes gives a pmf, e.g., dpois(). But dunif() is a pdf.
Sorry for the typo. Michael On Mon, Nov 7, 2011 at 12:08 PM, R. Michael Weylandt <michael.weyla...@gmail.com> wrote: > In short, the unif() distribution corresponds to the continuous > uniform distribution, not the discrete. > > Longer: dDIST() doesn't give a pmf so summing it isn't what you are > looking for: it gives a pdf. For punif() consider P\{X <= 1\} when X > is distributed on [1, 10]. Clearly this has probability zero because > it can only occur for one out of uncountably many values -- though > this notion should be made more precise using a little bit of measure > theory. > > Michael > > > On Mon, Nov 7, 2011 at 11:49 AM, michele donato > <michele.don...@wayne.edu> wrote: >> Hi, >> I am trying to use dunif and runif >> however, I have two problems: >> if I do >> >> dunif(1:10, min=1, max=10) >> >> I get 10 values, which summed give me 1.1111 >> I understand that the probability is computed as f(x) = 1 / (max-min) >> but in this case it looks wrong: I have 10 values, each one >> equiprobable, and the probability for each one should be 0.1 and not >> 0.11111 (which is, consistently with the definition, 1/9) >> >> It looks like one of the extremes is not considered in the computation >> of the probability, but then it's assigned a probability anyway. >> >> Similar problem with punif. >> >> if I do >> punif(1, min=1, max=10) >> I get 0 as result, as if the lower extreme is not considered, which is >> not consistent with the description where min <= x <= max >> If the lower extreme is not considered because cdf(x) = p(X<x) {and >> not p(X<=x)} the problem stands in p(X<11) which should be the sum of >> everything. ( P(1) + P(2) + ... + P(10) ) >> >> What is happening here? >> >> ______________________________________________ >> 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. >> > ______________________________________________ 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.