fastest R platform: follow-up and summary

4. profiling of the program.

This was suggested by Profs. Ripley, Bates, Lumley and Andy Liaw. But
according to Prof. Ripley, it can only be done on unix system. For my
program I knew the bottleneck. It was just hard to break it.

Might still be worth a try.  I ran the profiler on this example in R
1.2.1 and found that around 90% of the time was in the call to outer.
Outer is quite a general function and doesn't perform as well as it
might in this special case.  If you use the R code analogous to your
ox code, that is replace

    sum <- sum + outer(ran, ran);	  

with

   sum <- sum + ran %*% t(ran);

then I get a factor of 7 speedup in this example.  That still leaves
it about 25 times slower than Ox, but it is certainly a worthwhile
improvement.

[I believe 1.3 should include an improved version of outer, but the
current version only has the potential of about a factor of 2 speedup
in this example; don't know if we'll get a chance to tune it further
before 1.3 is released, but this example does show that further tuning
would be useful.]

luke

Luke Tierney
University of Minnesota                      Phone:           612-625-7843
School of Statistics                         Fax:             612-624-8868
313 Ford Hall, 224 Church St. S.E.           email:      luke at stat.umn.edu
Minneapolis, MN 55455 USA                    WWW:  http://www.stat.umn.edu
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