Author: Tony Werten
Date: 23:46:48 12/12/01
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On December 12, 2001 at 18:31:14, martin fierz wrote: >aloha, > >there was a discussion about this, deep down in a thread about who is the best >chess programmer, so i decided share our experience here: > >thomas lincke (lincke_at_inf.ethz.ch) has generated an opening book for my >checkers program with a technique called dropout expansion. he wrote a paper on >this, i think. for checkers it works very well, my book is very close to what >you expect from reading human opening books. the book has 1.1 million scored >positions in, which gives me about 200'000 book moves. Im using a different approach in XiniX. It's giving decent results but I'm not completely happy with it yet. I take a large collection of grandmastergames and play a game. At some point the last move of this game is not in the book anymore. I add this last move if the result for this current game is different from the result from the game I just diverted from. The "result from diverted game" can be a minimaxed result. You can minimax the scores and number of positions for getting a "percentage of winning games". The idea is 1) that the depth of the book is variable and 2) I don't want to add moves to positions I only know winning (or losing) games from. Following from 1 and 2 is that the book doesn't grow too much. Disadvantages: It sloooooow and you have to find a way of identifying "stupid" moves ( or hope grandmasters don't make stupid moves). Tony > >tom also used crafty as an engine to try and build a chess opening book. while i >do not know all details, i know he had at least a million nodes, and the book >was (if you ask me, 2200 rated) completely useless. > >the big difference in performance for the two games is that checkers has a very >high percentage of losers in every position. chess on the other hand has lots of >positions where you can make nearly any move. take the opening position, i play >1. b2-b3. or even 1. h2-h3. these moves are not the best, but they don't hurt >too much either. so the problem is, you cannot discard these moves, and that is >what dropout expansion is about - test all moves to some depth and throw out all >which you think lose, and defer expansion of all slightly inferior moves, and >move on in the best nodes. > >i thought maybe this technique would work in chess for some special variations, >where many moves are forced, so i suggested the dragon after about 15 standard >moves involving a pawn sacrifice for white - result: no use again. here's why: > >1.e4 c5 2.Sf3 d6 3.d4 cxd4 4.Sxd4 Sf6 5.Sc3 g6 6.Le3 Lg7 7.f3 0-0 8.Dd2 Sc6 >9.Lc4 Ld7 10.0-0-0 Tc8 11.Lb3 Se5 12.h4 Sc4 13.Lxc4 Txc4 14.h5 Sxh5 15.g4 Sf6 > >[D] 3q1rk1/pp1bppbp/3p1np1/8/2rNP1P1/2N1BP2/PPPQ4/2KR3R w - - 0 16 > >this was our starting position. i had hoped that in a sharp position as this, >dropout expansion would also work for chess. it didnt :-( >the problem was that crafty's main line went like 16. Qh2? h5? etc. the correct >answer to 16. Qh2? is Rxc3! which every dragon player will play in a slpit >second. the problem is that even if you can take the queens off with white now, >your position is bad. there have been too many discussions here about >"understanding", and i don't really want to say anything about it to avoid >further discussion. let me define "understanding" for this purpose as "does the >evaluation function know that this position is good or not", so that it "knows" >it *without* using the search? if a program's evaluation function does not >know/"understand" that the black position here is ok, it will never produce a >sensible main line, because the essential features of this position will not >change for a long time to come - black is an exchange down but has a pawn and >white's pawn structure is cripplede and his king is not safe. about all which >can change in the next 20 ply or so is that the queens come off, and even then >black is just fine. > >so, to conclude this post, i believe in automated book generation for games with >few good moves/position but i don't believe in it for chess. tom also used it >for awari to good effect. i don't know enough about chinese chess, i played a >couple of times in beijing, but more for fun :-) > >cheers > martin
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