Most of the top engines are happy to sac the exchange or give up a pawn for positional considerations, but closed positions are still an achilles heel.
Top engines are sometimes willing to sac a full exchange for the "positional consideration" of weakening their opponents king position, but I suspect they often see through brute calculation that they are getting a very serious king attack. I don't recall any examples of them being willing to do so for more general positional considerations not involving a king attack (unless they also get at least a pawn back as partial material compensation). Can you cite an example of an engine and position that does not involve king hunts, sham sacrifices or partial material compensation?
Perhaps you guys could come up with some examples and post them.
I definitely agree with your comment. For some ancient examples, take a look here:
Newer Rybka versions are even much better at this.
> Top engines are sometimes willing to sac a full exchange
> for the "positional consideration" of weakening their opponents king position
Other reasons can also be seen in engine games, one example being a dangerous passed pawn.
>I don't recall any examples of them being willing to do so for more general positional considerations not involving a king attack (unless they also get at least a pawn back as partial material compensation). Can you cite an example of an engine and position that does not involve king hunts, sham sacrifices or partial material compensation?
I could show many examples. Here is one which is beautifully played by Rybka 2.3.2a 64 2CPU against Deep Shredder 11 x64 2CPU. This is a game from the CEGT 40/120.
Black is a pawn up in this position. Rybka has the white pieces and starts by sacrificing the exchange: 26. Rxe4! Bxe4.
And now Rybka continued with 27. Nxf7! Kxf7
Rybka is a rook down at the moment, but the knight on c7 cannot be defended: 28. Bf4 Qd8 29. Rxc7+ Kg8
The fireworks are over and Rybka is a full exchange down. Black's main problem is that the rook on h8 is out of play. So here we have yet another type of "positional consideration" for sacrificing the exchange. The game continued 30. Qb3 Bf5 Black could probably have held on to the material advantage longer with 30...Qf6, but White's initiative would also pay off in the end in that case. 31. Be5 Rh7 32. Bc4 Kh8 33. Bxe6
White wins back a pawn, but he still needs one more pawn to restore the material balance! 33...Qd3 34. Bxf5 Qxf5 35. Qd5 Qf8 36. f4 h4 37. f5 Re8 38. Qxa5
Finally we have material equality (at least in the "classical" sense. Larry will probably count differently :)), but White has an overwhelming position and went on to win the game. Rybka's evaluation of this position is +3.23 at depth 21. For comparison it's evaluation of the position before the exchange sacrifice 26. Rxe4! is +0.64 at the same depth:
[+0.64] d=21 26.Rxe4 Bxe4 27.Nxf7 Kxf7 28.Bf4 Kg8 29.Rxc7 Qf8 30.Bc4 Bf5 31.Qd7 Qf6 32.Qb5 Rh7 (0:02.26)
Here is the game in PGN format:
[Event "CEGT 40/120"]
[White "Rybka 2.3.2a 64 2CPU"]
[Black "Deep Shredder 11 x64 2CPU"]
1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 e6 5.e3 Nbd7 6.Bd3 dxc4 7.Bxc4 b5
8.Bd3 Bb7 9.e4 b4 10.Na4 c5 11.e5 Nd5 12.O-O cxd4 13.Re1 Be7
14.Nxd4 Qc7 15.Bd2 Nxe5 16.Rc1 Qb8 17.Bb5+ Kf8 18.Nc5 Bxc5 19.Rxc5
a5 20.Bf1 h5 21.h3 Kg8 22.Rb5 Ng4 23.Nf3 Ngf6 24.Ne5 Nc7 25.Rc5
Ne4 26.Rxe4 Bxe4 27.Nxf7 Kxf7 28.Bf4 Qd8 29.Rxc7+ Kg8 30.Qb3 Bf5
31.Be5 Rh7 32.Bc4 Kh8 33.Bxe6 Qd3 34.Bxf5 Qxf5 35.Qd5 Qf8 36.f4 h4
37.f5 Re8 38.Qxa5 Rd8 39.Qb5 Qe8 40.Qc5 Qf8 41.Qc4 Re8 42.Qd5 Rxe5
43.Qxe5 Rh6 44.Re7 Kh7 45.Qe4 Rf6 46.Qxh4+ Kg8 47.Qe4 Kh7 48.Qxb4
Rxf5 49.Qe4 Kh6 50.a4 Rf1+ 51.Kh2 Qf4+ 52.Qxf4+ Rxf4 53.a5 Ra4
I searched both for "active" and "passive" exchange sacrifices (don't know what the correct terms are). By "active" I mean sacrifices like the typical Rxc3, but by "passive" I mean sacrifices where you allow the opponent to win the exchange by capturing the rook with a minor piece. An example is playing Rd5 where it can be captured by a minor piece. Here are more such examples:
This position is from a game Rybka 1.0 64-bit - Chess Tiger 2007, CCRL 40/40. Here Rybka played 13. g3 and Black captured the rook: 13...Bxf1. White didn't get any material compensation for the exchange, but placed the knights on d5 and f5 and then created a passed pawn on the queenside.
[Event "CCRL 40/40"]
[White "Rybka 1.0 64-bit"]
[Black "Chess Tiger 2007"]
1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e5 6.Ndb5 d6 7.Bg5
a6 8.Na3 b5 9.Bxf6 gxf6 10.Nd5 Be6 11.Bd3 Rg8 12.O-O Bh3 13.g3
Bxf1 14.Bxf1 Be7 15.c3 Rb8 16.Nc2 Rg6 17.Nce3 Kf8 18.Nf5 Kg8
19.a4 Bf8 20.axb5 axb5 21.Ra6 Na5 22.b4 Nc4 23.Bxc4 bxc4 24.Qe2
Qd7 25.Qxc4 Kh8 26.Qc6 Qe6 27.b5 Qe8 28.Qxe8 Rxe8 29.b6 Rb8 30.Ra7
Rg5 31.b7 Rxf5 32.exf5 Kg7 33.Nb4 d5 34.Nc6 Rxb7 35.Rxb7 Bd6
36.Nd8 Kf8 37.Nxf7 Be7 38.Nh6 Ke8 39.Ng8 Bd8 40.Rb5 Kf7 41.Rxd5
Bc7 42.Rd7+ Kxg8 43.Rxc7 h5 44.c4 Kf8 45.Rd7 Ke8 46.Rd5 h4 47.c5
Ke7 48.c6 Kf7 49.c7 Kg7 50.c8Q hxg3 51.h4 gxf2+ 52.Kxf2 Kh7 53.Rd7+
Kh6 54.Qh8# 1-0
This position is from a game between Ktulu 8.0 and Rybka 2.2 32-bit 2CPU (CCRL 40/40). Rybka ignored Ktulu's threat to capture the rook on d8 and played 18...d5 which resulted in being a full exchange down. Rybka won the game.
[Event "CCRL 40/40"]
[White "Ktulu 8.0"]
[Black "Rybka 2.2 32-bit 2CPU"]
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 g6 6.Be3 Bg7 7.h3
O-O 8.Bc4 a6 9.O-O b5 10.Bb3 Bb7 11.f3 Qc7 12.a4 b4 13.Na2 e5
14.Ne2 a5 15.c3 Na6 16.Ng3 Rfd8 17.Rc1 Qe7 18.Bb6 d5 19.Bxd8
Rxd8 20.Qc2 Bh6 21.Rcd1 d4 22.cxd4 exd4 23.Bc4 Be3+ 24.Kh1 Nd7
25.Nc1 Rc8 26.Nge2 Ne5 27.b3 Qf6 28.Nd3 Nxc4 29.bxc4 Nb8 30.Nb2
Nd7 31.Nc1 Ba6 32.Nb3 Nb6 33.c5 Qh4 34.f4 Nd7 35.Nd3 Bb7 36.Nf2
h5 37.c6 Rxc6 38.Qb2 Rc3 39.Nxd4 Nc5 40.Nf3 Qf6 41.Rfe1 Kg7 42.Ne5
Nxa4 43.Qa2 Ra3 44.Qxa3 bxa3 45.Rxe3 a2 46.Ra3 Qb6 47.Rxa4 Qxf2
48.Ra1 Qxf4 49.Nf3 Bd5 50.Nd2 Be6 51.Nf3 Qb8 52.Rg1 Qb5 53.Rd4
In this position (Rybka 2.2 64-bit 2CPU - Hiarcs 11.1 2CPU, CCRL 40/40) Rybka played 16. Rd1 and Hiarcs grabbed the exchange with 16...Bxe5.
[Event "CCRL 40/40"]
[White "Rybka 2.2 64-bit 2CPU"]
[Black "Hiarcs 11.1 2CPU"]
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.g3 e6 7.Bg2
Qc7 8.O-O Nc6 9.Re1 Be7 10.Nxc6 bxc6 11.e5 dxe5 12.Rxe5 O-O 13.Bf4
Qb6 14.Na4 Qa7 15.Qe2 Bd6 16.Rd1 Bxe5 17.Bxe5 Nd5 18.Bd4 Qc7
19.c4 Ne7 20.Bb6 Qb7 21.Bc5 h6 22.Nb6 Rb8 23.Qe5 f6 24.Qd6 Re8
25.b4 e5 26.b5 axb5 27.cxb5 Nf5 28.Qd3 Nd4 29.Bxd4 exd4 30.Bxc6
Qxb6 31.Bxe8 Bg4 32.Qc4+ Be6 33.Qc6 Bxa2 34.Qxb6 Rxb6 35.Bc6
d3 36.Rxd3 Bc4 37.Rd4 Be2 38.Rb4 Kf8 39.f3 Bd3 40.Kf2 Ke7 41.Ke3
Bc2 42.Rd4 Bf5 43.Ra4 Kd6 44.Ra7 g6 45.Kd4 Rb8 46.Rf7 h5 47.Rxf6+
Ke7 48.Ke5 Bd3 49.Re6+ Kf8 50.Kd6 Bxb5 51.Kc7 Bc4 52.Re4 Bb5
53.Kxb8 Bxc6 54.Re6 Bb5 55.Rxg6 Kf7 56.Rg5 Be2 57.Re5 Bd1 58.Rd5 1-0
how did you find these games - did you look through the games manually or do you have software that does this for you
much appreciated. :-)
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