Author: Amir Ban
Date: 14:22:19 02/12/99
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On February 12, 1999 at 01:57:01, Komputer Korner wrote: >In Henri Arsenault's Games Domain review of Fritz 5-16 bit he states that "After >each variation is analyzed, the hash table is emptied, so this is a much more >efficient way to analyze a game." I say Oh REALLY ???!!!!!!!!!! >Any correct hash table info (even a full one) is better than no hash info. When >the hash table is full, programs implement a replace hash algorithm which >determines ( many programs have 2 hash tables or even 3 if you count the pawn >hash table) which hash entries get knocked out. If a hash entry is not there >(got knocked out) and that position at the same depth comes up again, then the >program of course has to calulate the score over again. BUT if it doesn't get >knocked out then time is saved. That is the whole purpose of a hash table. I >realize that initializing the hash table takes cpu time, but whether the hash >table is full or empty at the beginning of the move should not affect this. >Therefore I wonder why the Fritz and Junior engines do this. Don't they play a >little weaker because of this practice? >-- >Komputer Korner Common sense tells me that if there's a loss, it's small. Assuming the transposition table was generated when it was last the program turn to play, when it's again our tun to play, we are now two plies deep in the old tree. Assuming a branching factor of 6, I would expect then that only about 1/36 of the old transposition table contents is still relevant, and even this part is of limited use because the depth draft in those entries is now smaller (by typically 2 ply) from what is needed in the new search. My conclusion from this is that the previous table is only about 1%-3% as effective as it was on the search when it was generated (previous move). I think the transposition table is the element of computer chess that is most consistently over-valued. (Second place goes to the opening book). Amir
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