>What komi did you use? It is nice to have the sgf in addition to the position.
It is 7.5, and I do not have the SGF. I will try to create SGF for future posts, to make reproduction easier for all. >Could it be that Pebbles have trouble seeing that the semeai is won >after white C9. Yes, exactly. Pebbles has no code (in either search or playouts) for winning semeais of more than one move. No pattern that identifies C9 as a good move for O. There is code that finds C9 for X: it is a winning snapback. There is no code that tries to play the opponent's move, so the knowledge does not transfer from one color to the other. What rule proposes C9 in Many Faces or Valkyria? 1 2 3 4 5 6 7 8 9 A - - - - - - - - - B - O O O O X X X O C - X X X O O X O - D - O - X O X O O - E O - O O X X O X X F - O X X X X X O - G - X X - - O X O - H X O O O - - X X O J - - - - - - - O - On the face of it, C9 doesn't put O ahead in any semeai. After C9, O is behind X's B8 string by 3 liberties to 2, and O is behind X's E8 string by 2 liberties to 2 with X to move. >Anyway I entered the position manually with komi 7.5, and Valkyria >plays C9 right away winning the semeai in the upper right corner and >after that white wins 0.5 even if black gets everything else. C9 is winning, but it isn't so obvious as Magnus suggests. There are several complexities to see through. 1) O wins the semeai on top only if O moves first. After X's A8, O must find A6, A5, and A7. Those moves must be played in that order, because if X plays A8 and A6 then X wins the semeai because O cannot play A9, which is self-atari. 2) If O tenukis at any time, then X wins by playing F9 or G9, followed by capturing O's F8/G8 string, and atari with D9. 3) In a random-play game, the fact that X has 2 sequences versus 1 (i.e., F9 or G9 for X versus only A6 for O) makes up for the fact that O gets to move first. So it is vitally important to have code in the playouts that handle the semeai more accurately for O than purely random. 4) Magnus says "wins by 0.5 even if Black gets everything else" but that's not right. O must also win the semeai at left. In a random-play game, O would lose that battle fairly often. The principal way to lose is X C1, O tenuki, X D3 (atari), O E2, X F1 (atari), O G1 and a Ko fight for life. 5) The Ko fight there is a picnic for X, since X was counting on losing anyway. It follows that X will gain a move in the battle of his choice, so O will only win if his tenuki was played in the semeai at upper right. I think that to play this situation completely right you must have playout policies that specifically drive success in semeais and/or ko. Those successful policies do not have to be right for the right reason. For example, if you play C9 because you believe that it is the only move that has a chance of winning the semeai against E8/E9, then you are right for the wrong reason, because there is no way to win against E8/E9; C9 just happens to win against another string. Without heuristics that specifically drive success, the combination of multiple battles make matters combinatorially worse. For example, the dynamic in Pebbles is for the moves that win the semeais to be the second, third, fourth or higher move generated. This is not so bad if there is only one battle. But when multiple battles are joined, X can play a forcing move for a turn in another battles, and then return to the other side. It is a dynamic version of the horizon effect, where bad effects are first pushed out, and then delayed by bad move ordering. I think that working on this position will yield several advances in move ordering. I have already found the snapbacks, and I think there will be others. Brian _______________________________________________ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
