[Gridflow-dev] feature request: [#shuffle]

[Claude Heiland-Allen]

Hi all,

Mathieu Bouchard wrote:
> On Wed, 11 Jan 2006, Claude Heiland-Allen wrote:
 >
>>I'm working on something, and would find it really handy to have a
>>[#shuffle] object that would take an input grid's 'vectors' and swap
>>them with each other to give a random permutation.

After heading down a completely wrong direction, I've managed to get it 
working the way I want it to (which maybe is slightly different to the 
way I specified in my original mail):

"( 3 4 5 # ... )" -> [#shuffle 0] => shuffle in blocks of ( 4 5 # ... )
"( 3 4 5 # ... )" -> [#shuffle 1] => shuffle in blocks of (   5 # ... )
"( 3 4 5 # ... )" -> [#shuffle 2] => shuffle in blocks of (  1  # ... )

Two points:

1. this error message when feeding Dim[0] to [#reverse] can be ignored, 
but it is annoying:

error: ArgumentError: [#reverse]: factor=0 should be >= 1
base/grid.c.fcs:149:in `void GridInlet::set_factor(int)'
[#reverse]

2. I got into a horrible place with [fork] and undefined behaviour, so I 
used an abstraction wrapping it with [#store] and [#finished] - you 
might not want to feed huge grids into [#shuffle] for this reason.

> [42 # 1000000000}
>  |

You missed a [# rand] here.

> [#grade] generates a uniformly random permutation of numbers 0..N-1
>  |
> [#outer ignore (0)] add dimension to please #store
>  |
> [#store (42 # ...)]
>  |
> random permutation of 42 values

Ok, I got what I wanted to do working with this method.  Statistics and 
probability were never my strong points.

>>inlet 0 method grid (grid(d0 d1 d2 ... dN) grid)
> 
> the convention is that the last dimension is labeled d(N-1) so that the 
> number of dimensions is N instead of N+1.

Ok, that's much more sensible :-)

> do you need it to be faster than the one using [#grade] above?

I don't know yet...


Claude
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