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

[Blake McBride]

Why not use random(3) (or are you)?

Thanks.

Blake

On Wed, Aug 20, 2014 at 9:07 AM, Juergen Sauermann <address@hidden> wrote:

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