[Computer-go] Chinese vs Tromp-Taylor rules

Petr Baudis pasky at ucw.cz
Fri Mar 6 11:12:50 PST 2015

On Fri, Mar 06, 2015 at 10:25:14AM +0100, Urban Hafner wrote:
> Now my question is what exactly do I have to do to implement chinese rules?
> If I understand the differences correctly, the only difference between TT
> and Chinese are (I somehow couldn't find any mention of positional super ko
> in the TT rules on Senseis <http://senseis.xmp.net/?LogicalRules>, but IIRC
> both use PSK):
> 1. Suicide isn't allowed in chinese rules
> 2. Dead stones are removed before scoring in chinese
> Now #1 is simple and I've already implemented it as it's used by CGOS, but
> how would I handle #2? I guess it needs to be a reasonably fast as it
> should be used even in the playouts. It seems like a rather difficult and
> error prone approach, or is there a quick way to find groups that are 100%
> alive?

(1) is correct.  (2) is too, but it is of course not mandatory; if you
capture these stones, the score does not change even under Chinese
rules, so you may just follow the same procedure as in TT rules.

In the tree, to determine whether it's safe to pass and identify dead
stones, a simple trick is to simply keep running statistics of average
ownership of each point in final playout positions.  If it's the
opponent's color 90% of time, you may assume it's dead.  (And this
statistics can be useful for other purposes later too.)

Ad superko, the rules say "(6) A turn is either a pass; or a move that
doesn't repeat an earlier grid coloring." which is indeed positional
superko, same as in Chinese rules.

A pitfall to remember - in handicap games, handicap stones don't count
in favor of black's score!

> The alternative would be to continue using TT rules internally and just
> play until there are only single point eyes left on the board.

Thta's what Pachi does, and I believe many other programs too.
We prevent multi-stone suicide only in the tree, not in playouts,
for performance reasons (which might have became completely dubious
meanwhile, though).

				Petr Baudis
	If you do not work on an important problem, it's unlikely
	you'll do important work.  -- R. Hamming

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