[R] flipping a plot vertically?

[Tim Brown]

Hi,

This seems like an obvious question but I can't find the answer in 
the "par" help document --- I'd like to make a plot where the 0,0 
point is in the top left of the screen rather than bottom left... . 
This is just a regular plot that is flipped vertically -- i.e.  the 
x-values will run along the top of the plot and the y-values will go 
from the top left (0,0) to the bottom left (0,ymax) --  I assume 
there is a simple way to do this but I can't find it.
Any suggestions?

Thanks!

Tim