On Oct 27, 7:06 pm, Stuart Halloway <[EMAIL PROTECTED]> wrote:
> ; take samples, tracking number that land
> ; :in circle and :total number
> (defn sample-for-pi [count]
> (reduce (fn [{in :in total :total} point]
> {:in (if (in-circle? point) (inc in) in)
> :total (inc total)})
> {:in 0 :total 0}
> (take count (repeatedly random-point))))
You'll need to use a different pseudorandom number generator /
pseudorandom stream for each thread. Otherwise adding more threads
won't help performance much, because they will serialize on the PRNG.
(Hopefully Java thread-protects the PRNG's state -- the C library
doesn't, which makes for interesting errors ;-) .) Using Pthread
mutexes to protect the thread state, in a C implementation of a Monte
Carlo method on an 8-core 2-socket recent Intel box, I was only able
to get 2x speedup. (For game tree search I can get 8x speedup on the
same machine.)
Check out the following parallel PRNG tutorial for more info:
http://www.cs.berkeley.edu/~mhoemmen/cs194/Tutorials/prng.pdf
mfh
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