Re: [computer-go] Position Rich in Lessons
Quoting Brian Sheppard sheppar...@aol.com: 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? C9 is not treated in a special way. I guess in this case it is AMAF that finds it and play at te root level. I use the same code to bias the tree part as I use for the playouts. In the playouts a lot of tactical code for pruning bad suicidal moves and playing forced moves (when the number of liberties in the semeai is 2 or less) are used. I can also be that Valkyria finds C9 for X quickly if O does not play it. 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. Your analysis is correct. And to me it just appears quite obvious. And as David point out it is not physical liberties that are counted but the move necessary to play. 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. The O must win the semeai is also obvious. What I meant is that O can let X start ko fights and win them as long O just captures the large X block. 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. Valkyria does nothing intelligent when it comes to ko and wins always in this position. But this is because white can let black win all small ko fight as long as all important semeais is won. So in this position only semeai knowledge is necessary. But you might try to decrease the komi, because then white will have to win with a larger margin! That could make the position much harder to read out correctrly. 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. Are you talking about move ordering in the
[computer-go] Position Rich in Lessons
I am analyzing an interesting position, shown below. It is rich in lessons, at least for me, so I figured I would share it. By the way, I have a simple way to find interesting situations. When Pebbles loses, it saves the *last* position that it thought it was winning (i.e., the rating of the selected play was 0.5). Many such positions occur late in the game, which always means that critical tactics are mishandled by the playouts. Here is the position: 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 - White (O) to play. There are several battles going on here: 1) The X string on C2 is locked in a semeai with the O group below. X loses that battle regardless of the side to move. 2) The O group on the bottom middle does not have enough room to make life. It is dead in alternating play, except when it connects to the O group on middle left. Connecting depends on winning a Ko on G1, and O should always lose that Ko in alternating play, but in random play O often survives. 3) The bottom right group of loose O stones is pretty much always killed off. But while alive those stones have aji because they take way liberties of the X string on E8-E9. 4) Finally, we have the semeai on top right. The X string on B6 has 3 liberties, and the O string to its left has 2 liberties, so it seems that X should win regardless of who moves first. Taking this altogether, X wins well over 45 points, so X should win this game. But Pebbles (playing O) showed O as winning this situation something like 75% of the time, even though Pebbles had to resign in just a few more turns. The variations showed that Pebbles easily solves any one of these battles, but the position as a whole is hard because at least two of those battles are always pushed into the playouts. The playouts do respect alternating play in local battles, so the wrong winner often emerges. As payoff for reading this far, here is the first lesson from this situation. I have been adding rules that inhibit self-ataris. In this position, X has a vital tactic that *requires* a self-atari: X plays on C9 to win O's C8 string in a snapback. The lesson is that if you inhibit self-atari then you should consider testing for snapback. Pebbles tests for snapback in the MCTS, where I am sure that it pays off. I have not yet tested what happens in the playouts. Further analysis convinced me that O is actually winning this game. My current engine likes A8 for O until iteration 7000, and then F9 for O, and switches to the winning move only on iteration 143,000. But it doesn't really see the win, because the evaluation remains around 50.3% no matter how long Pebbles searches. Best, Brian ___ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
Re: [computer-go] Position Rich in Lessons
Quoting Brian Sheppard sheppar...@aol.com: Further analysis convinced me that O is actually winning this game. My current engine likes A8 for O until iteration 7000, and then F9 for O, and switches to the winning move only on iteration 143,000. But it doesn't really see the win, because the evaluation remains around 50.3% no matter how long Pebbles searches. What komi did you use? It is nice to have the sgf in addition to the position. 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. Could it be that Pebbles have trouble seeing that the semeai is won after white C9. Valkyria expects black A8 after C9 which delays the capture of the white stones. Sometimes Valkyria has (or used to) problems evaluating such semeais. -Magnus -- Magnus Persson Berlin, Germany ___ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
RE: [computer-go] Position Rich in Lessons
Many Faces also plays c9 right away, with about 66% win for O, expecting A8 then A6. -Original Message- From: computer-go-boun...@computer-go.org [mailto:computer-go- boun...@computer-go.org] On Behalf Of Magnus Persson Sent: Monday, June 22, 2009 7:05 AM To: computer-go@computer-go.org Subject: Re: [computer-go] Position Rich in Lessons Quoting Brian Sheppard sheppar...@aol.com: Further analysis convinced me that O is actually winning this game. My current engine likes A8 for O until iteration 7000, and then F9 for O, and switches to the winning move only on iteration 143,000. But it doesn't really see the win, because the evaluation remains around 50.3% no matter how long Pebbles searches. What komi did you use? It is nice to have the sgf in addition to the position. 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. Could it be that Pebbles have trouble seeing that the semeai is won after white C9. Valkyria expects black A8 after C9 which delays the capture of the white stones. Sometimes Valkyria has (or used to) problems evaluating such semeais. -Magnus -- Magnus Persson Berlin, Germany ___ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/ ___ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
[computer-go] Position Rich in Lessons
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/
RE: [computer-go] Position Rich in Lessons
There is a book (2nd Book of Go, I think) that teaches how to count liberties in a semeai. Once O plays C9 it has far more than two liberties, since black has to play approach moves on either side to win the semeai. For example, black has to play 3 times to fill the liberty at D9, and black can never fill the liberty at A9. So O has at least 4 liberties after C9 is played. If you count semeai liberties correctly, it's obvious that white C9 group has more liberties than the black group (after C9 is played). So Many Faces can see directly that O wins the semeai after C9 is played. So a one ply search finds that C9 is a good move. Many Faces' heuristics then encourage the UCT search to try this move first, and it holds up well in the playouts. David -Original Message- From: computer-go-boun...@computer-go.org [mailto:computer-go- boun...@computer-go.org] On Behalf Of Brian Sheppard Sent: Monday, June 22, 2009 3:01 PM To: computer-go@computer-go.org Subject: [computer-go] Position Rich in Lessons 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. ___ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
[computer-go] position
About 2 months ago I sent a note to this email list about a research chair position and a postdoc position, both financed through the SHACRNET High Perfomance Consortium. The advert below does not have high performance computing as a requisite attached. But because it mentions discrete math, combinatorics and experience in computation as valuable strengths, this might be of interest to someone on the email list. Together with a few students we already have a small but active computer Go group at our math department. Thomas Wolf Prof at Department of Mathematics Brock University Ontario, Canada --- BROCK UNIVERSITY FACULTY OF MATHEMATICS AND SCIENCES MATHEMATICS The Department of Mathematics invites applications for a tenure-track appointment in an area of discrete and computational mathematics at the rank of Assistant Professor starting July 1, 2007. The Department offers an MSc in Mathematics and Statistics, has an innovative and unique B.Sc. Mathematics program called MICA (Mathematics Integrated with Computers and Applications) and plays a leading role in Mathematics Education. The successful candidate must have a PhD in Mathematics or related field by the time of the appointment, a proven record of or potential for research excellence, and an active research program that will attract external funding. Ideally, the candidate’s area of research would complement that of current faculty. The position requires undergraduate teaching including Combinatorics and Mathematics for Computer Science, graduate teaching, and supervision of graduate students. The successful candidate must demonstrate strong teaching abilities and a committed interest in the use of technology for the exploration, understanding and applications of mathematics. The appointment is subject to the availability of funds. The review of applications will start on February 28, 2007 and will continue until the position is filled. Applicants should send a curriculum vitae, an outline of their research plan and a description of teaching philosophies, and arrange for at least three letters of reference (one of which should address teaching) to be sent directly to: Chair of the Mathematics Search Committee Department of Mathematics Brock University St. Catharines, Ontario L2S 3A1, Canada E-mail: [EMAIL PROTECTED] In accordance with Canadian Immigration requirements, priority will be given to citizens and permanent residents of Canada. Brock University encourages applications from all qualified individuals including women, members of minorities, native people, and persons with disabilities. ___ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
