Hey there. In this game, white won by 0.5: https://online-go.com/game/12453335
I believe that this would be correct under Chinese rules. Black has 22 alive stones and 21 points of territory on the board (43 overall). White has 17 alive stones, 21 points of territory and 5.5 komi (43.5 overall).
In this game, white passed first. If I understand it correctly, under AGA rules, if white passes first and black passes second, white then has to pass one more time, giving another pass stone (i. e. one point) to black. Shouldn’t black have won this game by 0.5?
AGA rules for reference (the rule in question is #11: http://www.usgo.org/files/pdf/completerules.pdf )
Is there any difference aside from the label between games played under Chinese rules vs games played under AGA rules?
Counting by Area: When counting by area, the players add up their total area.
Prisoners are ignored. The player with the greater total area (after adjusting for
any compensation offered according to Rules 3 and 4) is the winner.
I would imagine this is why, since we use area counting for AGA rules automatically on OGS. Am I 100% on this no but I believe this to be the reason.
EDIT: I realized you aren’t forced to make another passed on OGS even with AGA scoring implemented but if the result of the Passed stones don’t change the outcome (If area scoring is used and passed stone mean prisoner rather than a solid point)
Counting by territory (assuming white actually passed once more as required by AGA rules):
Black captured 5 during the game, 2 dead at the end, 2 pass stones, 21 territory = 30 points.
White captured 3 during the game, 1 pass stone, 21 territory, 5.5 komi = 30.5 points.
Result is W+0.5 in agreement with the area counting (as it must be under AGA).
(Note that counting by territory without forcing white to pass last (ie count the game as it ended by territory) would reduce black’s score by 1, so the result would be W+1.5.)
A game under AGA rules can be counted either by area or by territory. For territory counting the extra pass stone matters, but for area counting it doesn’t. OGS implements area counting (which is often considered easier to program), so who passes last doesn’t matter.
Also, in AGA komi is 7.5 points, not 5.5… To answer your last question…
Both AGA and Chinese rules will always end up with the same score (by design.) AGA doesn’t always mesh with Japanese rules though because of the pass stone rule.
Thanks for clearing this up for me, Purble
@danielt1263 Source for AGA komi being 7.5 for 9 x 9 please…?
You already posted AGA’s official rules. Rule 3 shows the komi as 7.5 and makes no allowance for board size so the komi is 7.5 regardless of board size.
Hmm true. Good thing OGS enables us to choose komi as we like, I guess
True… Keep in mind though that proper komi (Chinese rules) for a 3x3 board is known to be 9 and I believe komi for a 5x5 board is 25. So don’t be so sure that komi for 9x9 is less than komi for 19x19.
You’ll be happy to know that I was, in fact, previously unsure about what 9 x 9 komi should be. Shouldn’t komi for smaller board sizes be higher?