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 <jgil...@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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