Thank you very much Jay.

2010/3/19 G. Jay Kerns <gkerns@ysu.edu>

> Dear Randall,
>
> On Fri, Mar 19, 2010 at 10:24 AM, Randall Wrong <randall.wrong@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
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>

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