Author: Vincent Diepeveen
Date: 05:35:07 05/06/01
Go up one level in this thread
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. 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 :) > "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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