Re: [Bug-apl] Bad quality of the roll function

[Juergen Sauermann]

Hi Kacper,

thanks for reporting this. Should be improved in SVN 439.

/// Jürgen


On 08/20/2014 06:47 AM, Kacper Gutowski wrote:
> Currently GNU APL uses LCG with modulus 2⋆64 and then reduces values modulo
> desired range.  This, beside being slightly biased for ranges not dividing
> the modulus, yields reduced periods when range is power of two.
>
>        ?10 16⍴16
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
> 11 2 13 12 15 6 1 16 3 10 5 4 7 14 9 8
>
> Doesn't look very random to me.
>
>
> -k