[blind-chess] Chess Article #32 Chess Computers and How They Work
- From: Roderick Macdonald <rmacd@xxxxxxxx>
- To: Blind Chess Mailing List <blind-chess@xxxxxxxxxxxxx>
- Date: Tue, 25 May 2010 22:38:07 -1000 (HST)
Chess Article #32
Chess Computers and How They Work
From: http://www.playe4.com/index.html
Playing chess requires acknowledgement of the game rules and
strategies, creativity, concentration, abstract thinking, visual
memory and other human characteristics. So, how come chess
computers often best human chess players, even chess grandmasters
as Gary Kasparov? To solve this mystery, we must understand how
chess computer work, or in other words, how a computer can imitate
the decision-making procedure of a human player (and still step out
with the upper hand).
Chess Computer Tree Search
Today's chess computers are rather complicated, and fast, very
fast. To simplify their action, let's use the tree allegory. The
tree represents the entire possible moves that can be executed by
the computer; the tree's branches illustrate all the legal moves,
and the leaves form the final positions. So, if the computer plays
White, at the start of the game it has about 20 possible moves:
moving either pawn one/two positions or moving any knight to two
separate paths.
Then, Black has to make one of the 20 possible responses to White's
first move, multiplying with 20 we get 400 possible moves for
Black, then 8,000 moves for white, etc. In short, you get quite a
gigantic tree before you get to the middle game, and even the
fastest and most advanced chess computers won't be playing in such
conditions, not even the slowest, most novice human player.
Computer Chess "Thinking"
Instead, the chess computer generates the predictable board
positions tree search. A fast computer can generate a ten-level
tree of positions (something like 10 trillion positions), a faster
one even a twenty-level tree and the fastest computer can manage
millions of board position a second. To win at chess, the computer
has to do more than just search for possible moves; it also has to
evaluate them, i.e. to sieve the ultimate moves out of the
seemingly endless forest possibilities.
Lacking the human mind, the chess computers have an evaluation
function, which can be as basic as chess pieces calculator to as
extensive as a formula that measures and weights the value of the
position while taking in consideration hundreds of influential
factors. Either way, the computer is guided by a certain number
that rates the value of the given board position.
Known as the "minimax algorithm", on its turn, the computer plays
the best possible move, responding to the opponent's worst possible
move. Though the computer plays in complete darkness and despite
the human brain's alleged superiority, results prove that the
program efficiency in beating the intellectual counterparts.
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