1. Computer chess

chess-playing programs essentially explore huge numbers of potential future moves by both players and apply a relatively simple evaluation function to the positions that result
- directed reading
in the early days of computer chess, 1950s it was thought that by studying how a machine could play chess we would understand how the human brain works
- alas this proved to be untrue
Claude Shannon wrote the first paper on computer chess in 1950
in his paper he mentions two techniques which could be used to solve this problem
- type A strategy - brute force looking ahead say 6 moves and applying the minimax algorithm (AlphaBeta was not discovered until a decade later)
- type B strategy - which examines only the interesting moves at each ply
he concluded that type B was the better technique
- time has shown the opposite!
- easier to compute all moves (type A), than write a program to work out the interesting moves - and faster..
Shannon estimated that with approximately thirty moves possible in a typical real-life position, he expected that searching the approximately (over 700,000,000) positions involved in looking three moves ahead for both side (six plies) would take about sixteen minutes, even in the "very optimistic" case that the program evaluated a million positions every second
- it took about forty years to achieve this speed

2. Modern chess programs

type B chess programs were abandonded in 1973 in favour of type A style programs
modern chess programs evaluate a full ply width of moves up until a certain level
- then they selectively reduce the width
- try and eliminate null moves (circular board positions etc)

one of the severe weaknesses of computer chess was in the end game
much work was done by Ken Thompson and others (1977 onwards) to explore check mate and the move before this
- and the move before this etc..
they found some supprising facts
- technically king and rook can draw against king and queen
- before it was generally accepted that king and queen could win
read the wikipedia entry for more details

in these notes the board will be labelled a-h along the x-axis and 1-8 along the y-axis

in Othello we have seen that a simple material evaluation function delivers a reasonably strong computer opponent
in Chess, just using material in an evaluation function requires an enormous amount of computing speed to deliver good results
- thus even the most powerful of chess computers use a more sophisticated evaluation function than just material advantage

calculates material

∞ king
900 Queen
500 Rook
300 Knight
300 Bishop
100 Pawn
maybe Knight are worth more than Bishops...
- maybe a Rook is worth two Knights...
- possibly these values should change over the stages of the game

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