Throwing in my 2 cents:
(def chunk-size 2000)
(defn sum-tree-part [nums start length]
(reduce
#(+ %1 (nth nums (+ start %2)))
0
(range length)))
(defn sum-partition[nums]
(reduce +
(pmap #(sum-tree-part nums % chunk-size)
(range 0 (count nums) chunk-size))))
; Save the vec and reuse it. Seems to take longer to create the vec
than sum it.
(def vec-range (vec (range 1000000)))
(println "sum-partition: " (sum-partition vec-range))
(dotimes [_ 5] (time (sum-partition vec-range)))
(println "sum-seq: " (sum_seq vec-range))
(dotimes [_ 5] (time (sum_seq vec-range)))
(println "sum-tree2: " (sum_tree2 vec-range))
(dotimes [_ 5] (time (sum_tree2 vec-range)))
Results:
sum-partition: 499999500000
"Elapsed time: 543.951 msecs"
"Elapsed time: 521.138 msecs"
"Elapsed time: 512.409 msecs"
"Elapsed time: 540.504 msecs"
"Elapsed time: 512.003 msecs"
sum-seq: 499999500000
"Elapsed time: 687.038 msecs"
"Elapsed time: 689.839 msecs"
"Elapsed time: 690.173 msecs"
"Elapsed time: 690.715 msecs"
"Elapsed time: 690.543 msecs"
sum-tree2: 499999500000
"Elapsed time: 809.912 msecs"
"Elapsed time: 829.039 msecs"
"Elapsed time: 823.197 msecs"
"Elapsed time: 820.383 msecs"
"Elapsed time: 821.239 msecs"
I have a 5 year old dual core computer. It would be interesting to see
if someone with more cores has a greater improvement over sum-seq.
-Matt Courtney
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