sampling from the uniform distribution over a convex hu

Ranjan Maitra writes:

Does anyone have a suggestion (or better still) code for sampling
from the uniform distribution over the convex hull of a set of
points?

This is implemented in library 'spatstat'.

If x and y are vectors of coordinates of your initial set of points,

   library(spatstat)

   W <- convexhull.xy(x, y)

  P <- runifpoint(42, W)

will compute the convex hull and generate 42 independent 
uniformly-distributed points in the convex hull.

Thanks, Adrian! I should have remembered about 'spatstat' after
the Baddeley et al. paper to the RSS in June 2005, where the
package was extensively used! (Though neither convexhull() nor
runifpoint() are in the package I downloaded at the time; but of
course things have moved on!).

But this brings me to another issue -- It seems that the "R Site
Help and Archive Search" at http://finzi.psych.upenn.edu has been
belly-up since at least Saturday (when I tried to use it to search
for relevant material for this query).

My browser says "connection refused", ping hangs, and traceroute
returns "!H" (host unreachable); and that is still the situation
this morning. I hope this is temporary, and not a withdrawal of
the service.

Anyone in the know?

With thanks,
Ted.

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E-Mail: (Ted Harding) <ted.harding at nessie.mcc.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 26-Mar-07                                       Time: 10:23:57
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