Author: Stuart Cracraft
Date: 18:13:33 01/11/98
I wanted to share my experience with the group regarding implementation of the pawn transposition table this weekend. It took about an hour to put in and another few hours to test. I do like the result. Now I just probe the table and if the score is there, use it, avoiding costly pawn structure evaluation, the bane of programmers, the preventer of positional play. On the Win-at-Chess suite, it is able to get the pawn structure score about 93% of the time from the pawn transposition table, avoiding calculation. There was a lot of pawn logic (backward pawns, pawn holes, attacks by pawn on the center, pawns in the center, wing pawn advances, .etc) that I had written but kept out of the evaluation function because it slowed down the search and resulted in worse scores on tactical suites. I tossed it back in and retested at WAC and there was no horrible slow-down. But, due to the tactical nature of WAC, this extra pawn evaluation logic, once running at normal program-speed without slowdown, was not helpful in getting a better score though. I suspect it might be more helpful in real games or positional positions like levers in Bratko- Kopec or the positional and endgame problems in Louguet II. One point: I don't clear the pawn transposition table between searches unless solving a problem suite on the theory that in a real game, the table will be filled with useful pawn structure evaluations. Actually it needn't ever be cleared since there is no real replacement scheme other than just over-write/replace-with-new, so having a few pawn structures in the table from any previous search is always better than having none. My experience with pawn transposition table has been positive; however I do not see 98% successful probes, only 93%, on average. --Stuart
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