Hi all,
The code below implements a Monte Carlo simulation to estimate the
value of pi. It works, and it was easy to reuse the original single-
threaded approach across multiple agents.
How idiomatic is this use of agents? Other than bringing in ForkJoin,
are there other idiomatic ways to parallelize divide-and-conquer in
Clojure?
Cheers,
Stuart
(defn in-circle? [[x y]]
(<= (Math/sqrt (+ (* x x) (* y y))) 1))
(defn random-point []
[(dec (rand 2)) (dec (rand 2))])
; 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))))
(defn guess-from-samples [samples]
(assoc samples :guess (/ (* 4.0 (:in samples)) (:total samples))))
; guess pi by running Monte Carlo simulation count times
(defn guess-pi [count]
(guess-from-samples (sample-for-pi count)))
; guess pi by running Monte Carlo simulation count times
; spread across n agents
(defn guess-pi-agent [n count]
(let [count (quot count n)
agents (for [_ (range n)] (agent count))]
(doseq a agents (send a sample-for-pi))
(apply await agents)
(guess-from-samples (reduce (fn [a1 a2]
{:in (+ (:in @a1) (:in @a2))
:total (+ (:total @a1) (:total @a2))})
agents))))
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