[R] 2 parameter exponential distribution

[Ben Bolker]

John Westbury wrote:
> Ben,
> 
> Say you have some variable (x) ~ exp f(x|lambda,theta) where f(x|lambda,
> theta) = lamba*(e^(minus lambda*(x-theta)))
> 
> Lambda is the inverse scale parameter and theta is a location parameter
> (I erred in calling theta a shape parameter in the original question). 
> 
> John

  Presumably P(x)=0 for x<theta?  In which case

dexp2 <- function(x,rate=1,loc=0,log=FALSE) {
   dexp(x-loc,rate=rate,log=log)
}

rexp2 <- function(n,rate=1,loc=0) {
   rexp(n,rate=rate)+loc
}


 etc.

  It turns out that dexp(x) gives 0/-Inf for x<0 (I thought it would
give a warning, but it doesn't), so this is relatively simple.

  Of course the next question is what you actually want to do with this
distribution ...

> 
> On Mon, Jan 11, 2010 at 4:23 PM, Ben Bolker <bolker at ufl.edu
> <mailto:bolker at ufl.edu>> wrote:
> 
>     John Westbury <jrwestbury <at> gmail.com <http://gmail.com>> writes:
> 
>     >
>     > Hello,
>     >
>     > I am new to R and am trying to figure out how to specify an
>     exponential
>     > distribution with scale and shape parameters.  I can specify an
>     exponential
>     > distribution with an inverse scale but would like to know how to
>     specify the
>     > distribution with a shape parameter as well.
>     >
>     > thanks much,
>     >
>     > John
>     >
> 
>      Do you mean a gamma distribution?  I'm unfamiliar with any
>     definition of the exponential distribution with more than one
>     parameter.  Can you point to a reference/example somewhere?
> 
>      Ben Bolker
> 
>     ______________________________________________
>     R-help at r-project.org <mailto:R-help at 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.
> 
> 


-- 
Ben Bolker
Associate professor, Biology Dep't, Univ. of Florida
bolker at ufl.edu / people.biology.ufl.edu/bolker
GPG key: people.biology.ufl.edu/bolker/benbolker-publickey.asc

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 261 bytes
Desc: OpenPGP digital signature
URL: <https://stat.ethz.ch/pipermail/r-help/attachments/20100111/d921c316/attachment.bin>