Author: Uri Blass
Date: 11:43:24 10/03/03
Go up one level in this thread
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
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