[computer-go] creating a "random" position

[George Dahl]

On 7/8/07, Paul Pogonyshev <pogonyshev at gmx.net> wrote:
> George Dahl wrote:
> > How would one go about creating a random board position with a uniform
> > distribution over all legal positions?  Is this even possible?  I am
> > not quite sure what I mean by uniform.  If one flipped a three sided
> > coin to determine if each vertex was white,black or empty, then one
> > would have to deal with stones with no liberties somehow.  Could those
> > just removed?
>
> As I remember from theory of probability, you can create such a uniformly
> "random" position this way[1]:
>
>   1. create a really random position, i.e. traverse all intersection and
>      assign a black/white/empty state at random to each;
>
>   2. if it happens to be not legal, discard and repeat step 1.
>
> I believe it should be very fast, and this mustn't be difficult to check.
> I.e. rate of discards should be low enough for speed of algorithm to be
> speed of step 1 times C, where C is small.
>
> However, this will tend to give you very artificial-looking positions.
> Whether it is fine for your use-case, you know better.
>
>   [1] http://en.wikipedia.org/wiki/Rejection_sampling
>
> Paul
>

I think this is what I want.  Thanks!  So I might have to repeat this
a few hundred times to actually get a legal position?
- George