Thanks that fixed it! On Jan 25, 2015, at 8:34 PM, Neil Toronto <neil.toro...@gmail.com> wrote:
> You can compute in log space using `log-gamma`: > > (define (my-permutations* n k) > (exp (- (log-gamma (+ n 1)) (log-gamma (+ (- n k) 1))))) > > I wouldn't trust the last four digits or so of large results, but that may be > accurate enough for what you're doing. > > If not, look at "math/private/flonum/flonum-factorial.rkt". I'm pretty sure > you can just copy the code, remove the integer checks, and have something > that works. (Test it, though.) Error should be <= 3 ulps if you do that. > > Neil ⊥ > > On 01/24/2015 01:18 PM, Alexander D. Knauth wrote: >> Is there a way to define a function for a generalization of permutations for >> flonums using gamma? >> This doesn’t work because if n is >=171 and k is a float it just returns >> +inf.0: >> #lang racket >> (require math/special-functions) >> (define (my-factorial x) (gamma (+ x 1))) >> (define (my-permutations n k) (/ (my-factorial n) (my-factorial (- n k)))) >> >> Is there a better way to do this without it returning +inf.0, or is there a >> library function anywhere that does this? >> >> >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
