Author: Robert Hyatt
Date: 08:30:55 04/08/03
Go up one level in this thread
On April 08, 2003 at 11:16:24, Uri Blass wrote: >On April 08, 2003 at 10:57:21, Richard Pijl wrote: > >>On April 08, 2003 at 10:04:02, Uri Blass wrote: >> >>>[D]8/5pp1/4p1kp/1Q6/2rqP2P/8/5PP1/5RK1 w - - 0 27 >>> >>>This position happened in a game of movei. >>>For the game see http://f11.parsimony.net/forum16635/messages/46511.htm >>> >>>I found that latest movei also suffers from the same evaluation problem. >>> >>>Movei evaluates the position as almost equal. >>> >>>I found that Crafty and a lot of programs understand that black has a clear >>>advantage(more than 0.5 pawns for black from the >>>first iterations). >>> >>>I understand that black is better but the question is what factor in evaluation >>>helps a lot of programs to understand it. >>> >>>I can explain reasons to give advantage for black from program point of view: >>> >>>1)The black king is more advanced and it is known that the king should >>>be at the last rank except endgames. >> >>I don't agree. After h5+ the black king is locked out from the immediate action >>and has to retreat to h7. > >I understand it but piece square table gives h7 worse score >than g1 for the king except endgames. Yes, but the piece square table (in crafty anyway) is a _small_ part of the score for a pawn or piece. It is really intended to be a "tie-breaker" and nothing else, so that if all else is equal (it rarely is) then the best piece-square value will break the tie. > >I did not ask for opinion of humans but how do programs know it. > > >> >>>2)The white pawns are more advanced so by piece square table they >>>get bigger bonus after a move like h5+. >> >>But that would increase the white score? > >Yes >Piece square table give bigger score for the side that >it's pawns are more advanced. Same comment again. Piece/square table values in Crafty are nothing but tie-breakers. The main positional scores are based on lots of other considerations, with the pc/sq values breaking a tie when two different positions seem to have the same non-pc/sq scores. > >> >>I think you can detect black's advantage with three eval terms: >>- Limited mobility of the white rook. It cannot leave square f1 because of >>immediate threats on f2. > >I understand it but the question is if program understand it. >Moei use number of moves to evaluate mobility and f1 is only slightly worse >than possible sqares of the black rook. Then something is wrong with the way you are counting mobility. Mobility along the first rank is _far_ less important than mobility along an open file, or along your opponent's 2nd rank (your 7th rank). If you are just counting squares you can move to, that is probably the problem. I don't do mobility for all pieces, as there are other terms that produce similar effects. IE rook on an open file means a rook has mobility along that file, for example. > >>- Black has two attacking pieces, White only one. > >Movei does not count attackers and I do not know if this is an important factor. Two pieces attacking squares around the king, being close to the king, is an important factor. three pieces is even more important. This is a "second-order" evaluation term that has to factor in interrelationships among the pieces. > >I think that the important factor is weaknesses of the white pawns. The score was not a pawn structure issue, as the score output showed. Pawn structure is in the "pawn evaluation" line which was +.06 (good for white but just barely). >Here is another position when I think that black >has no advantage inspite of Crafty's opinion. It is the same issue. Black pieces vs white pieces. Open files. 7th rank. pieces attacking the king. Etc... > >[D]8/5pp1/6kp/1Q6/2rq4/7P/5PP1/5RK1 b - - 0 1 > >Uri > >Uri > > >>- Black has easy access to the 2nd row, increasing pressure on the white king >>position. >> >>Richard.
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.