[R] Sweave: Variables in code chunk headers

[Michael Hoffman]

I would like to be able to do something like this:

   <<echo=F,fig=T,width=mywidth>>=
   ...
   @

with mywidth set in a previous code chunk. Is there a way to do this in 
Sweave?

(Sorry for two questions in a row, I have been saving these up.)
-- 
Michael