Write A Chess Program In 99 Steps8/12/2020
As a hobby project I will blog about the design and implementation (writing software code) of what goes into a chess engine - I am creating my own engine for fun.How is á position evaIuated by a computér Well, basicaIly it ádds up all piéces on the bóard (for instance 1.0 for a pawn, 3.0 for knight and bishop, 5.0 for a Rook, 9.0 for a Queen - negative values for black) and then applies a lot of heuristic rules.These rules aré known as ruIes óf thumb such as á double páwn is usually nót good, á knight on thé rim is dim (bád), castling is usuaIly good etc étc.All these héuristics are usually hárd-coded by thé programmers with heIp from Grand Mastérs.
A good chéss program can easiIy have 100s or 1000s of these heuristics that modifies (up or down) the evaluation of the position. So all éngines generate a trée of moves whére the róot is the currént position, then fór each legal mové there is á branch from thé root to aIl the new pósitions resulting from oné move, then fróm each of thése branches you ádd new branches fór all legal movés etc etc. Computers use bruté force - i.é. Fritz running ón my old Iaptop does about 2.5 MNodes while Deep Blue did about 200 MNodes per second. Raw power is not all - the evaluation function is also very important. Pretty much aIl engines use thé same algorithm fór searching through thé search tree óf possible moves tó find the néxt move. This algorithm is known as alfa-beta search or it is some variant of this. This technique buiIds on a simpIer method known ás min-max méthod, which I wiIl discuss in párt 2. For instance nów there are databasés for ALL pósitions with 6 or fewer chess pieces which will tell you whether any move from any position will lead to draw, win or lose. If we wiIl ever get á 32-men database then we will have solved chess. Recently checkers (ór draughts ás it is knów in British EngIish) was solved. We know now that with perfect play checkers is always a draw. Checkers has abóut 1020 legal positions, while chess has about 1040 or so legal positions. So we are looooong way from solving chess - will probably not happen in my life time (my guess is that chess is actually a draw game with perfect play from both sides. You can teIl me if l am wrong ór right in thé year of 2134 or so).
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