How to Beat Chess Computers!

How to Beat Chess Computers!

KingsEnemy
KingsEnemy
Dec 22, 2009, 8:43 PM |
1

How to Beat Chess Computers

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This guide to beating Chess computers might help you to win a bit more often against Chess computers. A few things that really help are to be able to understand how they work and think, be able to predict what sorts of things they might not spot and to understand what parts of the game a computer is better than humans at playing.

HOW THE COMPUTER DECIDES WHO IS AHEAD

A Chess computer assesses who is ahead in a slightly different way to how many human players would. The piece values are the same but not all humans would consider some of the other factors that a computer does. A computer uses the following sort of scoring algorithm (these figures can vary from computer to computer):-

Queen = 9 points
Rook = 5 points
Bishop = 3 points
Knight = 3 points
Pawn = 1 point
King = Between 41 and 200 points - this varies from computer to computer, but it needs to be large enough so that it isn't exchanged off by mistake. 

Doubled Pawns = -0.5 points
Isolated Pawn = -0.5 points
Backward Pawn = -0.5 points

Any available move = 0.1 points as it is better to have more available moves than your opponent.

Factors such as weak pawns near the king should be penalized.

Well placed pieces, passed pawns, certain attacks and pins should be added to the score.

The computer subtracts your score from its own score. A positive score means the computer is ahead and a negative score means that the human is ahead.

OPENINGS

A good Chess computer will have a large openings database. For more common openings such as the Ruy Lopez, Giucco Piano, Queen's Gambit and the Sicilian Defence a computer will have a database containing up to about white and black's first 20 moves of many variations of these openings.

Therefore a computer will not need to use up any time at all if the human opponent sticks to the moves in the computer's database. This will give the computer much more time in the middle and endgames to do larger and deeper searches.

One possible tip is to play an unusual opening that will not be in the computer's database. This makes the computer start using up its time right from the start of the game, which will mean it can't search to as large a depth as it could if it knew the opening later on in the game. So if you happen to be an expert on the Hippopotamus Defence or some other unusual opening then you will probably know that opening better than the computer does, which could give you a bit of an advantage when the computer is doing large searches which is using up its time early on. It only takes one move not in its database and the computer will need to start doing large searches early in the game.

An example of this is supposing the time limit of a game is 40 moves in 2 hours before the time control. If the computer can play the first 20 moves directly from its database, it will then only have to start doing searches for move 21 onwards. Therefore it will only have to make 20 moves in the 2 hours which is about 6 minutes a move on average. But if the computer only had about 5 moves of a particular opening in its database then it will have to make 35 moves in 2 hours which is about 3 and a half minutes a move on average. This greatly reduces the search depths that the computer is able to do which will obviously reduce the standard of play that the computer is playing of the rest of the game quite considerably.

MIDDLE GAME

For a Chess computer the middle game begins as soon its opening database can no longer be used. In the middle game there are usually about 30 to 40 moves possible on each move. This is known as the branching factor and the larger this is then the larger the search needed. 

When the computer is searching for moves, it will therefore need to search about 1000 positions for one move from each player, 1000000 positions for two moves from each player, 1000000000 for three moves from each player and so on. The depth of the search then really depends on the speed of the computer and on the amount of time it
has available to move.

The search algorithm that most of the more modern Chess computers use is called the Selective Iterative-Deepening Search. This searching algorithm searches all possible moves to a depth of one first, then all possible moves to a depth of two, then all possible moves to a depth of three and so on.

If the computer calculates that there is a Checkmate or a loss of its queen for example then it terminates that branch of the search. This means that the computer doesn't have to continue searching a large number of moves from that branch, so it can use its memory to search to a greater depth on other branches of the search tree. 

A tip is that if for example you sacrificed your queen knowing that in three moves time you could get checkmate using other pieces then that branch of the tree might get terminated by the computer before it realises that its just fell for a mate in 3 which it now can't avoid. Some computers might not fall for this however as the very best computers would still have continued searching that branch of the search so this is a very risky plan.

The depth that the computer searches to depends on how much time it has left. Looking at the example from the openings above about the computer having less time if it doesn't know the opening, this might reduce a search from about 12 plies to 10 plies (where 1 ply is a move from one player, 2 plies is one move from each player) on each move. This could help reduce the standard of play of the computer.

One thing that better computers do is think during your time. If you therefore take about 15 minutes on one move you may find that the computer has already searched that move to a depth of about 13 plies. So a tip is to try and avoid taking this long over a move unless it really is necessary to take this long.

TRANSITION TABLES

Some of the better Chess computers use transition tables. They are used to remember some of the best lines from its previous searches and recent positions. So if you had a position and then two moves later that exact position was repeated then the computer would still have the best moves still stored in memory in a transposition table.

A tip then is try to avoid repetition (unless you are playing for 3 move repetition to get a draw) as the computer will probably have a recent position stored in memory and will be able to move instantly, which gives it more time to search on other moves.

END GAMES

Chess computers have databases of all 3, 4 and 5 piece endgames so they often don't need to use up as much time as you might expect them to in the endgame. An endgame like this favours the computer because of its database and also the branching factor on each move is reduced once pieces like the queens are exchanged off, so the computer can search to a greater depth than in the middle game while still using the same amount of time as it would in the middle game. Deep Blue can sometimes do searches of up to a depth of about 40 plies in the endgame while chess programs that you may use at home such as Chessmaster might search up to a depth of about 20 plies on its highest skill levels.

A tip is to try your best to avoid exchanging off pieces unless it really does help out your position. The branching factor on each move should be kept higher to force the computer into doing shorter searches on each move.

SUMMARY

These are some of the key points about Chess computers and how to beat them.

1. Playing an unusual opening will reduce the depth of the searches made by the computer in the middle game.


2. If you avoid exchanging off pieces unnecessarily then the computer has to do larger searches, which won't be to such a large depth.


3. Think about sacrifices that might benefit you if the computer accepts them and doesn't search that branch far enough to see what your plan really is. Be careful with this though as some computers will continue to search all branches.


4. Against better computers, the longer you take over a move, then the larger the search the computer might have already done before you even moved.


5. Unless your end game is excellent avoid endgames whenever possible as Chess computers can do extremely large searches in the endgame.

 

6. Avoid repetition of moves as this allows computers which use transition tables to save a lot of time as they can move instantly when they already have the position and best moves to play stored in a transition table.