Author: Dana Turnmire
Date: 09:01:08 05/05/01
Here is an interesting article found in a 1989 CCR article. "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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