Author: Albert Silver
Date: 06:55:46 12/09/05
It hardly seemed possible that Rybka "slightly positional" could improve on the score of the default "very positional" settings against Chess Tiger 15, having scored 30.5-9.5. Sure enough, it couldn't, but nor did it do much worse, scoring 29-11, conceding 3 more draws. 1 Rybka "slightly positional" +21/-3/=16 72.50 29.0/40 2 Chess Tiger 15.0 +3/-21/=16 27.50 11.0/40 I haven't checked the games other than the few I actually saw it play. I will say this much, and it is something I must say I have never said about any engine to date: I honestly get the feeling I could improve just by watching it play. It's not perfect, and I won't even mention the well-documented endgame oddities, but the piece maneuvers and placement, not to mention pawn play... Really something else. Here is one move that oddly enough struck me not only as typical of Rybka, but illustrative of its difference. [D]1k6/1p5R/2p5/P2b4/3P1K2/5P2/P7/8 w - - 0 55 White is completely won, so you'll wonder why I even bother showing it. The fact is that it played 1.a6! bxa6 and then 2.a3. This doesn't make the position more won by any means (if you know what I mean), but it shows the focus of the engine. It chucked the pawn in order to guarantee the king remains cut off on the 8th, and these 'little' things about piece placement and enemy restriction are a big part of its success IMHO. I've seen a number of sequences where a key behind a move it made was to prevent the opponent from doing something positive such as improving piece activity or just placement. Here is another pearl that I found remarkable: [D]rn3rk1/2pb2q1/3p1b1p/pPpPppn1/2N4B/PQN2P2/4B1PP/1R3R1K w - - 0 22 Rybka played 1.b6! here, a move that may not seem so unusual in itself, and one that no doubt other engines may find. What is striking is the sequence and 'idea' behind it. CT15 played 1...cxb6 sure enough, but contrary to expectations (including my own), Rybka didn't take back on b6. Instead it played 2.Nb5!!, a really striking move. It practically forces the exchange of Black's light-squared bishop, after which White will stand a lot better. Obviously, White will win back its pawn, but above all, it has removed a good defensive piece (note the bishop on d7 was one of the only to successfully communicate between both wings) and made it easier to penetrate. I'm not saying this wins the game by any means, I'm just saying it is a strong move that is completely atypical of computer programs. Match conditions were: Athlon64 Sempron 3400+ Hash: 256mb; ponder off Time Control: 10 mins + 2 secs Nunn2 Openings set. The next opponent, chosen according to the CEGT results, will be Hiarcs 9 as it scored far better than expected. The games are in a separate post. Albert
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