Author: Robert Hyatt
Date: 18:43:37 05/06/01
Go up one level in this thread
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... > >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... > >> "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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