Author: martin fierz
Date: 03:52:30 02/16/03
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On February 15, 2003 at 22:23:00, Robert Hyatt wrote: >On February 15, 2003 at 08:29:54, martin fierz wrote: > >>i was thinking of implementing position learning in my checkers program, and was >>trying to find out how this is typically done. if i understand it properly, >>here's what people do: >> >>1) if the search returns a value much lower than the previous search (define >>"much lower" as you like), write this position with it's value to the learn-file >>on disk. >>2) before every search, stuff positions from the learn file in the hashtable. >> >>this all sounds sensible to me, and i can see that this helps. however, i have a >>stupid question about it. let's imagine that in the initial position A your >>program is worse and decides to sac some material for a last-chance attack. a >>few moves later, in position B, it may think that it's compensation is not >>sufficient and drop it's score and learn this position. another 2 moves later it >>suddenly sees that it has a perpetual check, and that the move in position A was >>not to blame at all. i think this scenario is not quite unrealistic, and it >>seems to me that position learning doesnt work here, because you only learn that >>position B was bad (when in fact it wasn't). even if you were writing ALL >>positions to disk after searching them (something i would like to do in >>checkers), then you still haven't solved the problem: in your next search at >>position A you will have a hash hit at position B telling you that the correct >>move is bad, because you can't see further than your hash hit. >> >>hmmm. is there any workaround for this? >> >>cheers >> martin > > >This is a well-known issue, and I should add that position learning doesn't >claim to solve everything. It is really a defense against repeating the same >game multiple times which humans have been known to do. But as you notice, it >will not solve every kind of position, because of local maxima issues. IE >there are some holes you can not climb out because to do so means you first >have to go for a _lower_ score, to reach the valley floor and start to climb >up the other side... thanks for the answer. i was afraid i was missing something, but that doesn't seem to be the case then ;-) cheers martin
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