Author: Inmann Werner
Date: 13:40:02 01/26/99
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On January 26, 1999 at 11:01:27, Andrew Williams wrote: >On January 26, 1999 at 10:05:09, KarinsDad wrote: > >>On January 26, 1999 at 05:12:09, Andrew Williams wrote: >> >>>On January 25, 1999 at 18:30:20, KarinsDad wrote: >>> >>>> >>>>I don't understand. Couldn't you just as easily find positions that had castling >>>>in the TT way before you actually castle in your position? What is so special >>>>about castling? Is it that the number of transpositions drop drastically after >>>>castling (even though some would still be there)? Also, wouldn't castling often >>>>be within opening book moves so you are not yet in your TT? >>> >>>Sorry, I wasn't being particularly clear here. What I mean is that after I >>>castle, I change the pawn scoring to reflect the side the King is now sitting >>>on. So the pawns on that side are told to stay put, while the ones on the >>>other side are allowed to advance (this is a simplification, of course). So >>>I clear the TTs because the scores from before castling are not compatible >>>with those after castling. >>> >>> >>>Andrew >> >>Wow! What a good idea! Probably wouldn't have figured this one out on my own in >>a long time. >> > >I wish I could claim credit for this, but I think crafty (and probably >everyone else!) does this too. > >>With this in mind, do you also modify the pawn information within the search >>tree once you castle there as well (i.e. 6 ply down, it castles, hence the >>evaluation function should have a pawn modification below that node which is >>different than the pawn structure information, I assume you are using a >separate pawn structure evaluation)? >> > -------------- I have little problem following this English text.:) But I also had problems with my pawn hashtables while changing from midgame evaluation to endgame evaluation. At first, I cleared the hash table when i came into the endgame. But the last moves before reaching the endgame often got bad, cause the hashtable did not match the evaluation. So I decided to use 2 pawn hash tables. One for the middle game and one for the endgame. So I can look always in the right table during the search. It made the play more consistant. Werner ----------- >No. But this was my original intention. I didn't do this because.... >Oh dear, I've forgotten now. I think it was something to do with the way I >hash my pawn scores. The hashing only takes into account the location of >the Pawns, so I can't include any scoring that depends on the location of >the pieces. (It's coming back to me now). The original idea here was to >have different pawn scoring in the endgame (try to get them to promote) from >in the opening and middlegame (try to get them to stand still long enough >so that I don't get mated). So, I devised a different piece/square table for >my pawns once I reach the endgame, but "reaching the endgame" is dependent >on how many pieces are on the board. If I try to switch halfway-through the >search, it will mess up my pawn hashing (which I don't want because my pawn >TT gives me a big speed boost). So I switch piece/square tables at the root >of a search. While I was doing this (endgame piece/square tables), I thought >it would be a good idea to have different ones to reflect where each side has >castled - and I just incorporated this idea with the other. > >There is a slightly modified approach that would include the King's position >in the pawn hash key. Then any scoring relating to the King that doesn't >depend on other pieces (eg pawn shelter around the king) can be included in >the score that is put in the pawn hash table. This would allow me to switch >during the course of a search. This was being talked about here a few months >ago, and I think that Ernst Heinz said he did this. I'm pretty sure that it's >in crafty too. > >I hope this is clear (it's a bit "stream of consciousness", I'm afraid). I'm >really glad you asked the question, because you reminded me that I've only >done half of what I was thinking about doing. > >From the hints you've dropped, your program sounds like an interesting project. >Any idea how long before it plays its first game? Are you going to play it on >the servers? > >Cheers, > >Andrew
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