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 <ro...@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 <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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