mara serrano <teachermara <at> yahoo.com> writes:
>
> hi,
> i'm new to R and i'm trying to port a quattro pro spreadsheet into R.
spreadsheets have optional lower and
> upper limit parameters on the beta distribution function. i would like to know
how to incorporate this
> with R's pbeta function.
>
> thanks in advance,
> mara.
I think (?) you may mean a beta distribution with
limits scaled other than the standard 0 and 1.
You will have to construct these yourself but it's
fairly easy to do, e.g.
dbeta.scaled <- function(x,shape1,shape2,min,max,...) {
x.scaled <- (x-min)/(max-min)
dbeta(x.scaled,shape1,shape2,...)
}
and similarly for pbeta.
For rbeta (and qbeta) the scaling has to go in the other direction.
rbeta.scaled <- function(n,shape1,shape2,min,max,...) {
min+(max-min)*rbeta(n,shape1,shape2,...)
}
I did something like this for Tiwari et al. (2006)
Marine Ecology Progress Series 326:283-293 (although the
paper doesn't include any R code).
cheers
Ben Bolker
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