Dear Randall, On Fri, Mar 19, 2010 at 10:24 AM, Randall Wrong <randall.wr...@gmail.com> wrote: > Dear R users, > > ?rgamma gives me : > > rgamma(n, shape, rate = 1, scale = 1/rate) > > rate: an alternative way to specify the scale. > > The Gamma distribution with parameters ‘shape’ = a and > ‘scale’ = s has density > f(x)= 1/(s^a Gamma(a)) x^(a-1) e^-(x/s) > > Should I understand that scale=1/rate ? Is it written somewhere ?
You are kidding, right? It is written 8 lines above your question, by my count. :-) Perhaps you meant rate = 1/scale. > > Then rgamma(n, shape=a, scale = s) should be equivalent to rgamma(n, > shape=a, rate =1/s). Yep: dgamma(2, shape = 3, scale = 4) dgamma(2, shape = 3, rate = 1/4) > > I don't find this very clear. > > Thanks for your help. > > Randall > The point is that some books (and software) parameterize by the 'scale', and a whole other bunch parameterize by the 'rate'. The reader (and user) always needs to be careful that the version used is the one expected. And the help file says that S doesn't have a 'scale' parameter at all. Just be careful, and you should be fine. And IMHO, given that the PDF of the density is shown it is reasonably clear as-is. Best, Jay *************************************************** G. Jay Kerns, Ph.D. Associate Professor Department of Mathematics & Statistics Youngstown State University Youngstown, OH 44555-0002 USA Office: 1035 Cushwa Hall Phone: (330) 941-3310 Office (voice mail) -3302 Department -3170 FAX VoIP: gjke...@ekiga.net E-mail: gke...@ysu.edu http://people.ysu.edu/~gkerns/ ______________________________________________ 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.
