Author: Anthony Cozzie
Date: 12:15:55 10/03/03
Go up one level in this thread
On October 03, 2003 at 14:43:24, Uri Blass wrote: >On October 03, 2003 at 13:27:20, Anthony Cozzie wrote: > >>On October 03, 2003 at 12:47:23, Uri Blass wrote: >> >>>On October 03, 2003 at 12:13:13, Anthony Cozzie wrote: >>> >>>>On October 03, 2003 at 12:03:49, Uri Blass wrote: >>>> >>>>> >>>>>I can detect every big threat by adding a special search after making null move. >>>>> >>>>>For example if I like to detect threats of at least 2.2 pawns I can do >>>>>val=-alphabeta(depth-4,-beta+219,-beta+220,...) >>>>> >>>>>if (val<=beta-220) >>>>>threatmove[ply-1]=1; >>>>>//ply-1 because I still did not undo the null move. >>>> >>>>small error here: beta should be replaced by eval, or you will have massive >>>>instability problems. >>> >>>If I am a queen down in the search and I threat to win a bishop then I do not >>>consider it as a threat because a threat is a threat relative to beta. >>> >>>I believe that Tord does the same(he replied that your example of threating the >>>queen twice by sacrificing material is solved by extending only big threats so >>>if you sacrifice a rook and a bishop the threat on the queen is not a big >>>threat). >>> >>>I think that the idea that an extension should not be dependent on beta is a bad >>>idea. >>>It is better to have stronger engine with stability problems and not >>>weaker engine without them. >>> >>>I prefer even not to care about using hash tables for pruning because my >>>experience told me that I cannot get significant gain there easily(I have a lot >>>of stuff that means that pruning or extension is not defined only by the >>>position). >>> >>>Uri >> >>in your code: >> >>Suppose the BM extension succeeds, and the node fails low. In other words, the >>program was using delaying moves to push a threat beyond the horizon, the BM >>extension stopped it, and it realized it was in trouble (a reasonable scenario). >> >>Then beta will be (say) 200 less than it was previously, and the threat might >>not be 200 less than beta any more, and your new re-search w/out the extension >>will fail high. etc. >> >>Being a queen down in the search (may) have very little to do with beta: example >>WAC#141, where beta is a mate score even though white is down a rook and a >>queen, and beta for black is -mate score even though black is up a rook and a >>queen. >> >>anthony > >I can agree with you that using beta may be a mistake because of the fact that >beta is changed after fail high but using the static evaluation is also >a bad idea. > >In the case of Wac141 I want to use instead of beta the last calculated score of >the position that is almost equality that has nothing to do with the fact that I >lost a queen and a rook. > >If I replace beta by eval I do not get it because I understand eval as the >evaluation of the position that I have(I evaluate every node) > >Uri What I am saying is very simple: what is a threat? Answer: a threat is the possibility, if the side to move passes, for the other side to significantly improve their position. In other words, do a null search with eval-200, and fails low, it means that if white passes black can get a position at least 2 pawns better than the current position. anthony
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