[racket] Using future and touch

 From: Joe Gilray (jgilray at gmail.com) Date: Thu Jul 25 00:34:05 EDT 2013 Previous message: [racket] Using future and touch Next message: [racket] Using future and touch Messages sorted by: [date] [thread] [subject] [author]

```So I should write my own (gcd   ) and (square?   ) functions?

I can try that, but isn't there a simple way to use threads?

Thanks,
-Joe

On Wed, Jul 24, 2013 at 7:47 PM, Robby Findler
<robby at eecs.northwestern.edu>wrote:

> When I run this, the future visualizer shows that gcd and square-number?
> block the futures. square-number? is implemented in TR and if you take it,
> you find that integer-sqrt also blocks the futures. I'm not sure if those
> functions can be made to run safely in futures or not.
>
> Robby
>
>
> On Wed, Jul 24, 2013 at 7:26 PM, Joe Gilray <jgilray at gmail.com> wrote:
>
>> I have a ProjectEuler problem that I wanted to speed up so I thought I
>> would try to speed it up with future / touch.
>>
>> I tried the following:
>>
>> ; function that searches for progressive numbers for a given range of b
>> values
>> (define (find-progressive-num b-start b-end b-incr lim)
>>   (for/sum ([b (in-range b-start b-end b-incr)])
>>     (let loopa ([a (add1 b)] [suma 0])
>>       (cond
>>         [(> (gcd a b) 1) (loopa (add1 a) suma)]
>>         [(>= (* a a a b) lim) suma]
>>         [else
>>          (let loopc ([c 1] [sumc 0])
>>            (define n (+ (* a a a c c b) (* c b b)))
>>            (cond
>>              [(>= n lim) (loopa (add1 a) (+ suma sumc))]
>>              [(square-number? n) (loopc (add1 c) (+ sumc n))]
>>              [else (loopc (add1 c) sumc)]))]))))
>>
>> ; ProjectEuler problem #141
>> ; n = q * d + r
>> ; q/d = d/r = a/b (where a and b are relatively prime)
>> ; so d = a*r/b and q = a^2 * r / b^2
>> ; since a and b are coprime r must be divisible by b^2 or r = c*b^2
>> ; substituting: d = a*c*b and q = a^2*c
>> ; n = a^3 * c^2 * b + c * b^2
>> (define (euler141)
>>   (define lim 10000000000)
>>   (let ([f1 (future (λ () (find-progressive-num 1 1000 2 lim)))])
>>     (+ (find-progressive-num 2 1000 2 lim) (touch f1))))
>>
>> Unfortunately this runs no faster than the sequential version.  I tried
>> using the future-visualizer but I couldn't understand what it was telling
>> me (I guess some operation is blocking).  I also tried finer grained
>> threads (one for each value of b), but that did no better.
>>
>> Can anyone give me some pointers to successfully using future / touch?
>>
>> Thanks,
>> -Joe
>>
>> ____________________
>>   Racket Users list:
>>   http://lists.racket-lang.org/users
>>
>>
>
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