sweave options with variable

thanks,
? It can work but not as elegant as I expect because it add extra code to
every chunk of code.
I have tried the cache for this purpose it works in most case but have a lot
of other problems so I decided to control it by myself.
I guess that sweave running R code before tex, so tex variable do not work
and need find something run before sweave and set the variable,
but it seems currently no way do that. Write my own Sweave driver is too
hard for me hope in the future someone can refine the sweave driver.
? best wishes