[R] Finding Lower Envelope of Points on a Plot?

[David Winsemius]

On Jun 30, 2010, at 2:05 PM, Asha Sharma wrote:

> Hi,
>
> I am looking for a way to find the lower envelope of points on a  
> plot, preferably specifying what percentage of points should be  
> allowed to lie outside the envelope. There must be a straightforward  
> way to do this, but I do not seem to be able to find it. I would  
> greatly appreciate any help.

You probably want something like the "lower half" of the convex hull.  
You should find quite a bit of code with your favorite r search engine  
on the topic of "convex hull".
-- 

David Winsemius, MD
West Hartford, CT