Author: Robert Hyatt
Date: 10:27:18 06/23/00
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On June 23, 2000 at 05:36:36, Adrien Regimbald wrote: >Hi, > >I have recently noticed a problem with Faile while performing play testing >before releasing the current version - > >It is properly detecting 3-fold repetition, but sometimes it misses it in the >following case: >A position has been seen before, and is searched to depth x. >The position comes up again. If Faile plays the same move, it allows the >opponent to play a move which makes it a draw by 3-fold repetition. >Faile's search to depth x goes immediately due to hash table matches. It begins >to search depth x+1, and suddenly realizes that its intended move will result in >a draw, because it has finally had to actually search now. Faile runs out of >allocated time after searching the PV move. Faile will then play the move >(since this is the move suggested at previous depths and there is no time to >search other root moves), and the opponent, of course, plays the repeat and >draws the game. > >This is very frustrating, and seems to be the only significant problem with >Faile's play so far in testing (other than some problems with book coverage, >which should be fixed when I take some time to create a nice book - the current >book is only being used so it has _SOME_ book ;P). > >I have been trying to figure out how to solve this problem, and I've realized >that I have to somehow "age" the hash table entries .. but I'm not sure as to >when I should do this in order to get it working both to full effect in >benefiting the search, but also not causing these problems with 3-fold >repetition. Looking at other sources has so far been fairly futile - some of >them don't do anything to combat this issue, some use much more complex hashing >schemes than I do, and I can't seem to find a clear answer to this problem. > >Does anyone have any suggestions for me? I am using a single table, with >replacements done if the current depth is greater than the depth in the hash >table. > > >Thanks in advance, >Adrien. This is a known hashing problem. Both repetition _and_ 50 move rule draws are are problem and cause the same thing to happen. You can either (a) ignore it or (b) include path information in the hash signature, which will solve the problem, but basically wipe out hash hits.
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