or you can also store it in a var:
(defn fib [n]
(if (or (zero? n) (= n 1))
1
(+ (fib (dec n) ) (fib (- n 2)))))
(time (fib 30)) ;; "Elapsed time: 265.472 msecs"
(def fib-memo (memoize fib))
(time (fib-memo 30)) ;; "Elapsed time: 222.122 msecs"
(time (fib-memo 30)) ;; "Elapsed time: 0.058 msecs"
(time (fib-memo 30)) ;; "Elapsed time: 0.042 msecs"
Leonardo Borges
www.leonardoborges.com
On Sat, Apr 13, 2013 at 4:46 PM, Cedric Greevey <cgree...@gmail.com> wrote:
> To get the benefit of memoization, you need to store the memoized function
> and use it again. (memoize fib-nocur) returns a function that contains an
> internal memory of past results. If you call (memoize fib-nocur) again you
> get a second function with an (empty!) internal memory. If you don't use the
> first one more than once you don't see any benefit from its memory.
>
> So, try this:
>
> (let [f (memoize fib-nocur)]
> (time (f 30))
> (time (f 30))
> (time (f 30)))
>
> and see if the second and third times are much shorter than the first one.
>
>
> On Sat, Apr 13, 2013 at 12:52 AM, Liao Pengyu <arise...@gmail.com> wrote:
>>
>> Hi, there. I have a question about the memoization in clojure.
>> I compare two functions to test the performance improvement of
>> memoization:
>> (defn fib [n]
>> (if (or (zero? n) (= n 1))
>> 1
>> (+ (fib (dec n) ) (fib (- n 2)))))
>>
>> (time (fib 30))
>> get the result:
>> "Elapsed time: 316.65 msecs"
>> 1346269
>>
>> And then test for memoization:
>> user> (time ((memoize fib-nocur) 30))
>> "Elapsed time: 308.729 msecs"
>> 1346269
>> user> (time ((memoize fib-nocur) 30))
>> "Elapsed time: 314.942 msecs"
>> 1346269
>> user> (time ((memoize fib-nocur) 30))
>> "Elapsed time: 308.657 msecs"
>> 1346269
>>
>> Seems no effect. Since I just test it in nrepl and have no experience
>> about using clojure in project, I wander was the memoization really works?
>> Look forward to your responses
>>
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