Author: Vincent Diepeveen
Date: 10:14:08 05/07/01
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On May 06, 2001 at 21:43:37, Robert Hyatt wrote: >On May 06, 2001 at 08:35:07, Vincent Diepeveen wrote: > >>On May 05, 2001 at 12:01:08, Dana Turnmire wrote: >> >>> Here is an interesting article found in a 1989 CCR article. >> >>Exactly the biggest misunderstanding in chessbooks is that 2 rooks >>are stronger as a queen. Even in most endgames a queen wins easily >>against 2 rooks. > >I wouldn't say in "most". I would say in "some". Two rooks can box up >a queen and make it impossible to win since the queen can't overpower the >two rooks without the help of the king... Please print the first 1000 positions crafty sees 2 rooks against a queen. You'll see a tactical mess. That's logical that it is a tactical mess as otherwise you would NULLMOVE. Then figure out who wins. A queen is superior in picking up hung material. > > >> >>However grandmasters only get the exceptions on the board, so if a >>GM gets 2 rooks versus a queen then *usually* the 2 rooks are stronger. >> >>My piece values are about this: >> pawn 1000 >> knight 3625 >> bishop 3675 >> rook 5800 >> queen 11750 >> >>However there are always things wrong in piece values. >> >>In the above values an obvious problem is that a queen is stronger >>as 3 pieces which is NOT true. >> >>Also 2 pieces in the above example are very close to rook+pawn. >> >>However i have special code for that to fix it :) >Why not just use normal piece values and fix the rest of the problems by >evaluation, rather than faking up oddball piece values? Crafty uses 1,3,5 and >9, and has _no_ problems recognizing that two pieces for a rook and pawn is >a bad trade, as is a queen for three minor pieces... I have mobility+activity+centercontrol+scanning of all of my pieces in DIEP. Rooks get huge mobility scores. A rook at 7th rank might easily get 2 pawns bonus for just activity depending upon the position. If 2 rooks get that at the 7th rank then 11.75 for a queen isn't so much suddenly... > > >> >>> "Most elementary chess textbooks assign relative values to the pieces, based >>>on pawn=1, as follows: N=3, B=3, (or 3+), R=5, Q=9 (or 9.5 or 10). Most chess >>>computers use these numbers in their programs; in fact they play a critical >>>role. But there are serious problems arising from relying on these numbers." >>> >>>The most glaring problem is the exchange of two minor pieces for a rook and >>>pawn. Any tournament player should know that the minor pieces are nearly always >>>superior, except in simple endgames. In the middle game they are fully equal >>>(or even superior) to a rook and two pawns, as I learned the hard way in the >>>1972 U.S. Championship against fellow Senior Master Greg Defotis. Yet many >>>chess computers, especially Fidelity's will give up the two pieces for a rook >>>and one pawn at the drop of a hat, and nearly always go on to lose. I discussed >>>this problem with Fidelity's programmers last year, but as the Excel68000 makes >>>this losing exchange with alarming frequency it is clear that the problem has >>>not been corrected. >>> >>> Other piece value problems are improper bishop or knight exchanges (a >>>Turbostar flaw), and unsound sacrifices of a knight for two pawns and meager >>>positional compensation (Mephisto Amsterdam). Fidelity machines tend to vive up >>>their queens a bit cheaply, while Novag machines (especially the Super >>>Constellation) sacrifice the exchange too readily. >>> >>> It is my opinion that many of these problems relate to the fact that the >>>accepted piece value tables were derived from endgame theory, and are not >>>accurate for the middle game, in which pawns are more expendable and minor >>>pieces more valuable. To prove this I ran a series of blitz games, using the >>>autoplay feature on the Mephisto Dallas, in which I removed a white knight and >>>three black pawns (not rook pawns), varying the choice of knight and pawns, >>>before starting the games. Black won 8-0! I raised the compensation to four >>>pawns, and black still won 3-1 (at 5 pawns they split two games). So it seems >>>clear that at least in the early stages a piece is worth at least four pawns, >>>unless king safety or center domination is involved. >>> >>> Apparently, Mephisto reached the same conclusion. In a major departure from >>>the Amsterdam program as well as all others, piece values were changed for the >>>Mephisto Dallas program to knight=4, bishop=4+, rook=6, and queen=11. Suddenly, >>>two minor pieces equal rook and two pawns (as they should), the exchange retains >>>its standard two pawn value, and the unsound piece sacrifices of the Amsterdam >>>dissapear. The major drawback is a tendency to underestimate sacrifices of a >>>minor piece for two king-protecting pawns, but this may be dealt with in the >>>future by heuristics. The endgame is not harmed because passed pawns receive >>>sufficient bonuses in that phase to reduce the effective value of minor pieces >>>to around three pawns. My only criticism is that the queen should probably rate >>>a tad higher or the rook a hair lower, since queen and pawn are usually superior >>>to two rooks. I predict that the Mephisto Dallas piece values will soon be >>>copied by other programmers, and I recommend them to those human players who >>>feel the need for numbers.
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