Author: Don Dailey
Date: 11:07:59 01/12/98
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You may not have a problem. A assume given a longer search your numbers will climb to the 95-99% range. Is your table pretty small? Now that you have ps hash tables there are lot's of wonderful tricks you can play. I store lot's of info in mine that the evaluation can use further, like locations of passed pawns and holes etc. - Don On January 12, 1998 at 10:49:20, Stuart Cracraft wrote: >The 93% table-probe match I mentioned before for pawn transposition >table was for discrete, unrelated positions, such as from a problem >suite. > >When the pawn tranposition table is not cleared between moves in >a regular game, I am getting typically 95-99%. > >I'm pretty sure of my hash function, however I'll try some other >things. Formerly, I just took a mask of the bits for the index into >the hash table. Recently I've done a modulo of the hash to determine >the index. > >--Stuart > >On January 12, 1998 at 00:07:20, Don Dailey wrote: > >>On January 11, 1998 at 21:13:33, Stuart Cracraft wrote: >> >>>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 >> >>There is more than likely a problem. 93% sounds more like a worst >>case situation, look for a bug. The first thing I would check is >>the quality of the hash function. This is the easiest thing to get >>wrong and is very non-intuitive. >> >>Here are some things that might explain your numbers: >> >> 1. You're testing with short searches. >> 2. You're testing the opening position or positions near it only. >> 3. Your hash table is pretty small. >> >>If one or more of these things are true you may be ok. Otherwise >>look at your hash function, your address calculation etc. Is your >>table size correct? Is your address calculation mask correct (assuming >>you are using the power of 2 method?) >> >>At the Dutch championship I had a bug in my hash tables. My >>random number table was constructed wrong (my fault) and we were >>effectively only using 1/8 of our hash table. Every 8th bit in each >>number was the same! This kind of bug is very hard to catch. It >>was quite a relief since I had been sensing something wrong with the >>program and could never put my finger on it. We think this had a >>lot to do with our bad results. >> >>- Don
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