Thank you very much Jay. 2010/3/19 G. Jay Kerns <gke...@ysu.edu>
> 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/ > [[alternative HTML version deleted]]
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