Author: Matthew McKnight
Date: 11:14:47 12/17/03
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On December 17, 2003 at 13:19:55, Alvaro Jose Povoa Cardoso wrote: >On December 17, 2003 at 12:01:19, Matthew McKnight wrote: > >>On December 17, 2003 at 11:52:33, Alvaro Jose Povoa Cardoso wrote: >> >>>Hi, all. >>>I saw several discussions in the past on hash table replacing schemes, optimal >>>hash table sizes, wich information to store there, etc. >>>But I don't remember any discussion about what positions are the best candidates >>>to store in the HT. >>>What most of us do is to store positions in wich the best move is a fail high >>>or, an exact score, wich is correct for move ordering purposes. >>>I was wondering if someone uses a different criteria for choosing positions to >>>store in the HT. >>>When in some middle game positions I see a drop in the hash table hits (below >>>15%) of my engine I sometimes think if there is a better way to improve the >>>transposition effect, if such a thing can be done. >>> >>>My best, >>>Alvaro Cardoso >> >>I'm not sure if this answers your question, but I use two tables. One of them >>is the normal, "depth-preferred" table. The other one is an "always store" >>table. If I am adding a position to the table, but the entry in the DP table >>comes from a deeper search I leave the deeper information and put this new >>information in the "always store table," replacing without prejudice. Then in >>the readPosition() function I first check the depth preferred, and if there is >>nothing there I look in the always store table. This makes a noticeable >>difference with HT performance. >> >>Matt > >Thanks Matt, >but my question is more in the line of how do we choose positions to try to >store in the HT. I don't remeber seeing a discussion about that here. >Currently we choose a position with a best move that caused a fail high or an >exact score (above alpha). I wonder if that is all we can do. > >Regards, >Alvaro You can also store a lower bound for positions that fail low, so that if you come to that position again, you can adjust your window if need be.
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