[racket] A problem with Windows 8?

I don't see how your function count-times implements the required algorithm.

Please explain.


On Mon, May 27, 2013 at 12:01 AM, Tomás Coiro <tomcoiro at hotmail.com> wrote:
> I'm trying to do this Rosetta Code problem:
> http://rosettacode.org/wiki/Average_loop_length
>
> Now, this is my code
> #lang racket
> (require (only-in math factorial))
>
> (define (analytical n)
>   (apply +
>          (build-list n (compose (lambda (x) (/ (factorial n)
>                                                (expt n x)
>                                                (factorial (- n x))))
>                                 add1))))
>
> (define (count-times x times)
>   (if (= 0 (random x))
>       (add1 times)
>       (count-times x (add1 times))))
>
> (define (test n times)
>   (/
>    (for/fold ((count 0))
>      ((i (in-range times)))
>      (count-times n count))
>    times))
>
> (define (test-table max-n times)
>   (displayln " n\tavg\ttheory\terror")
>   (displayln "-------------------------------")
>   (for ((i (in-range 1 (add1 max-n))))
>     (define average (exact->inexact (test i times)))
>     (define theory (exact->inexact (analytical i)))
>     (define difference (* (sub1 (/ average theory)) 100))
>     (displayln (format "~a\t~a\t~a\t~a%" i average theory difference))))
>
> (test-table 20 100000)
>
>
>
> Im not really worrying about the formatting of the output now, this is the
> result.
>  n    avg    theory    error
> -------------------------------
> 1    1.0    1.0    0.0%
> 2    2.00036    1.5    33.35733333333335%
> 3    3.00578    1.8888888888888888    59.12952941176472%
> 4    4.00412    2.21875    80.46738028169015%
> 5    5.0035    2.5104    99.31086679413636%
> 6    6.00016    2.7746913580246915    116.24603337041157%
> 7    7.01433    3.018138700711438    132.4058201283651%
> 8    7.9905    3.2450180053710937    146.23900350550514%
> 9    8.97363    3.4583157448856556    159.47977749778022%
> 10    10.03618    3.66021568    174.19641019624285%
> 11    10.97729    3.852372050737359    184.94885373023365%
> 12    11.96714    4.036073675098951    196.50449826604333%
> 13    12.96795    4.21234791295252    207.8556251283266%
> 14    13.99396    4.382029424383519    219.34883691404528%
> 15    15.09822    4.545807285147228    232.13506541140143%
> 16    15.97676    4.704258247072678    239.62336166263555%
> 17    16.99324    4.857870820801628    249.8083960412072%
> 18    18.00859    5.007063098992893    259.6637318914995%
> 19    18.941    5.152196200957448    267.62963329075353%
> 20    20.05709    5.2935845860009    278.8942950499325%
>
>
> the average loop length is too long, I'm worrying if the problem is my code
> or if it actually is Windows 8.
> I already got a different result with inexact numbers here:
> http://rosettacode.org/wiki/Percentage_difference_between_images#Racket
>
> My question would be first, is my code wrong? (mainly "count-times")
> If it isn't, do you guys get similar results? Could there be a bug in the
> windows 32-bit installation for Windows 8?
>
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