Author: Tom Kerrigan
Date: 08:21:33 03/24/00
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On March 24, 2000 at 10:48:04, KarinsDad wrote: >On March 24, 2000 at 00:23:38, Tom Kerrigan wrote: > >[snip] >> >>If you're talking about a situation that is not mate, i.e., positional >>advantage, then I think problems like this are virtually unsolvable. > >Not so. This is a limitation of using one PV. > >> >>My program will sometimes play e.g. Bd3 blocking its own pawn on d2. No matter >>what kind of penalty I have for this situation, my program will invariably play >>this stupid move. The reason is that it thinks it will move the bishop off of d3 >>later in the PV, so the penalty is never enacted. Very frustrating. >> >>-Tom > >Of course there is a solution, but it involves hanging onto older PVs. > >If a PV changes due to a different PV getting a better score, save off the old >PV. > >If a PV changes due to it's own score dropping, do not save it. > >If a current line comes within a certain delta of the current best score, save >it off. > >When you are about to make a move, instead of just taking the current best score >PV first move, look through your list of old PVs as well. Carefully examine your >main PV and any of the old PVs that have a score close to the main one (e.g. >within -0.2). Since you may be searching say 24 positions per PV and have maybe >5 or so PVs to search, this takes very little time. Have a list of "types of >situations" which you consider "bad". Count the number of bad situations that >show up in any of the positions within each PV and pick the PV that has the >fewest bad situations with the highest score (i.e. if you main PV has the bad >bishop and none of the other old PVs have any bad moves, pick a PV from the save >list with the highest score, etc.). > >Theoretically, a -0.2 pawn is not going to cause any tactical problems, but >examining your "main lines" after searching could enable you to avoid lines with >tactically look ok, but play some stupid move that could hurt you way beyond the >event horizion. > >The issue is not one of resolving these types of problems within the evaluation. >If you do it that way, you either have to stop searching once you get to one of >these situations or you have to live with it. The alternative is to search for >this type of thing once your search engine is finished. I prefer the latter >method. > >KarinsDad :) Interesting idea. Do any programs actually do this? -Tom
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