Review of Game 2: AlphaGo's new move and devastating aggression
At the press conference after the first game, Lee Sedol estimated himself to have a 50% chance of winning the second game. The main question is whether AlphaGo will play (now with black) as aggressive and offensive as in the first game.
|Lee Sedol concentrates before the start of the second game.|
Referee Fan Hui (left) watches.
Dia. 1: Game 2, after black 37 (circle, AlphaGo is black)
When Lee Sedol returns at the match table, he takes an unusually long time to answer and after only just forty moves in the game, he is already 20 minutes behind in thinking time compared to AlphaGo. Redmond: "He has clearly difficulties to handle such a strong move that he has never seen before. It is a new and unique move and Lee Sedol has to think about it. This is the reason why people become professionals".
Dia. 2: Game 2, after black 41 (circle, AlphaGo is black)
Lee Sedol prevents AlphaGo to build up a moyo at the upper center and leaves the option open to make some territory himself at the right side. However, AlphaGo keeps the initiative and with black 41 (circle in Dia. 2) the program creates possibilities to play on one of the triangles (Dia. 2). Thereby Alphago can try to attack the white stones while making territory at the lower side. In addition, this move of AlphaGo helps to build the center moyo and prevents a white extension at the bottom side.
Dia. 3: Game 2, after black 61 (circle, AlphaGo is black)
Dia. 4: Game 2, after black 81 (triangle, AlphaGo is black)
In response to white's invasion (square in Dia. 4) black doesn't respond with obvious moves either on top or to the left of the invading stone, but instead plays a very solid move at the outside (triangle in Dia. 4), removing any weaknesses there so that black will have all his hands free to attack the invading stone much more heavily and aggressively later on.
AlphaGo still maintains the initiave and forces too choose between: a) extending to the center to make there a living group and neutralize black's strong influence in the center, and b) to make a small living basis in the upper left corner with the great risk that black will become rock-solid at the outside and with that strength can try to cash in the built center moyo (Dia. 4).
Dia. 5: Game 2, after black 97 (circle, AlphaGo is black)
Dia. 6: Game 2, after black 101 (circle, AlphaGo is black)
Dia. 7: Game 2, after black 127 (triangle, AlphaGo is black)
Redmond: "the control of the flow of the game has been alternated between the players several times. However, while fighting in the center AlphaGo played brilliant moves which forced Lee Sedol into immediate actions and choices". And while Lee Sedol seriously threatened the territory at the upper side, AlphaGo doesn't seem to worry and just cashes in points in the center: "points are points and it is completely irrelevant where on the board these points are taken" Redmond continues.
Dia. 8: Game 2, after black 139 (triangle, AlphaGo is black)
But even after white's big move in the upper right (square in Dia. 8) which threatens black's territory at the upper right edge, black plays calmly in the center. Thereby threatening to cut off another little tasty trail from white (triangle in Dia. 8).
Dia. 9: Game 2, after black 151 (circle, AlphaGo is black)
Dia. 10: Game 2, after black 163 (circle, AlphaGo is black)
At this point in the game Lee Sedol is behind about five points (komi included) so if black is able to cut yet more stones from white's meanwhile disintegrated center group it is definitively end of story. And this is exactly what ultimately happens: white is cut off once more.
Dia. 11: Game 2, end position after black 211 (circle, AlphaGo is black)
While Lee Sedol played some obvious overplays (a move that is too greedy to make more points than the opponent, more than could be considered as reasonable on the basis of your opponent's strength) in the first match, this game it is a completely other story: Lee Sedol didn't play any overplays and showed the very best of his Go play while seriously considering AlphaGo as one of his strongest opponents until now.
Several new and interesting moves have been conjured effortlessly on the board by a very aggressively playing AlphaGo. Some of which initially were regarded as unreasonable, incorrect, or simply not working.
In an exceptionally big fight during the second half of the middle game, Lee Sedol was put under enormous pressure (Dia. 6 en 7).With clearly much too little time to calculate accurately all favorable variations and outcomes in this extremely complex, never before occurring Go position.
In the end, Lee Sedol quits while being defeated more or less with his own weapon: starting ultra complex, all-or-nothing fights and then to try getting decisive advantage during that battle. For many top professionals it remained unclear until the last part of the middle game what would be the outcome of this second game.
Demis Hassabis mentioned that from the second half of the game on, AlphaGo became more and more confident in victory from the midway point of the game (as is continuously monitored by it's probability theory of winning). Even though the professional commentators could not tell who was ahead at that stage in the game.
Lee Sedol explained afterwards: "Today, AlphaGo played a nearly perfect game: from the very beginning of the game I did not feel like there was a point that I was leading. While during the first game I was overwhelmed and surprised by AlphaGo's way of play, today I was startled and speechless about the extremely strong moves AlphaGo generated, some of which were unexpectedly well working out. Furthermore, AlphaGo, unlike yesterday, did not make any unreasonable or incorrect moves from the second part of the middle game until the end of the game".
Asked about any possible weaknesses of AlphaGo, Lee Sedol passed over the question to Demis Hassabis after first stating that "today I lost because I was unable to find and detect any weaknesses in the play of AlphaGo". Hassabis answered the question by stating that one of the goals of the match of AlphaGo vs. Lee Sedol is to find out if AlphaGo has any such weaknesses and to try to learn from them.
Go-prof Hong Minpyo (9p) confirmed that Lee Sedol and he afterwards have analysed every move of the second game for five hours. After the game, Lee Sedol was very confused about why he had lost this game. This post-game analysis and research probably helped Lee Sedol to recover somewhat.
Today, AlphaGo apparently has beaten Lee Sedol with unprecedented accurate force power and incredibly profound computations during the most complex phase of the game. Reaching the point at which many human top professional Go players, including Lee Sedol, were unable to confidently calculate and reliably assess the outcome of the complex variations possible.
Lee Sedol remarked that in the upcoming third game of the match he will have to focus and concentrate on the opening and first part of the game, to seek and exploit any weaknesses of AlphaGo in order to build a lead early in the game.
[Part 6: Review of Game 1: Lee Sedol underestimates AlphaGo's incredible fighting power]
[Part 8: Review of Game 3: Lee Sedol's opening mistakes due to enormous mental pressure]