Author: Tom Kerrigan
Date: 01:14:39 04/07/00
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On April 07, 2000 at 03:42:49, Jan Pernicka wrote: > 1) how to quickly identify repetition in the game tree (with help from > hash tables, probably) ? You can do it using the hash table. What you have to do is have a bit in every hash table entry signifying whether or not the position is currently being searched. Then, if you do a hash table lookup and the bit is set, you know it's a repetition and you can return immediately. What I do is simply look through the past moves and see if the hash key is repeated. This sounds pretty slow, but for my program it's a little faster than the hash table method. I have no idea why. It's actually not that slow, because a chess program keeps track of how many moves since the last capture or pawn push, so you only have to check that number of hash keys. (After a capture or pawn push, subsequent positions will obviously be different from previous ones.) > 2) when reading some info about Zarkov there were mentioned, without > explanation, techniques as "reduced depth search" and "threat heuristics" > - so how and when can they be used? > Note: They were not mentioned in any context so to include that text > here wouldn't be useful... It sounds like the info is talking about null-move, which does reduced depth searches. There is a way to use null-move for "threat detection." If your reduced depth search returns a mate score, then you know something funny might be going on, and you can do an extension or something. I don't do this myself, but I know some people who do. > 3) does "razoring" mean pruning in general (or even alfa-beta method)? No, razoring is when you do futility pruning at the last ply of your full-width search. I think most people don't like it. I tried it and all my test suite scores went way down, even when the futility threshold was pretty conservative. It just causes to the search to miss too much... -Tom
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