On Sat, Feb 02, 2013 at 06:28:09PM -0800, Alexandros Bantis wrote: > Hello all. I'm working through the Project Euler problems in Java, > Scala, & Clojure (trying to learn all three?!?). I notice that for one > particular problem, I use--more or less--a similar algorithm for all > three, but the clojure code runs about 20-30 times slower than the > java/scala versions. Does anyone have any idea why this might be? It > strikes me that it might have something to do with every? but I don't > know because I'm a newbie with Clojure.
Daniel Solano Gómez gave a very interesting talk last summer about numerical performance in Clojure: http://www.infoq.com/presentations/Crunching-Numbers-Clojure While there are many technical tips about boosting math performance, Daniel's overarching point is that the best speed boost is the _right algorithm_. For instance, this solution to the problem runs in ~2ms: ``` (def primes "This should be a lazy-seq of primes generated by a bit-sieve, but for this example the largest prime we need is 3!" [2 3]) (defn prime-factors [n] (loop [n n fs []] (if-let [p (first (for [p primes :while (<= p (int (Math/sqrt n))) :when (zero? (rem n p))] p))] (recur (/ n p) (conj fs p)) (conj fs n)))) (defn lcm "The lowest common multiple of a set of numbers is the product of the distinct prime factors in the set each raised to the power of the greatest occurence in a single number." [& xs] (let [fqs (map #(frequencies (prime-factors %)) xs)] (apply * (map (fn [p] (Math/pow p (apply max (map #(get % p 0) fqs)))) (set (mapcat keys fqs)))))) (time (long (apply lcm (range 2 21)))) "Elapsed time: 2.010032 msecs" 232792560 ``` I know you are explicitly asking for language implementation differences, but I believe you would be better served in this instance by studying more elegant algorithms. The fastest code in any language is the code that does not execute; designing with this in mind is especially important in Clojure, where the functional abstractions are beautiful, but somewhat costly. guns -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
