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Subject: Re: a question to Tord about detecting threats in null move

Author: Uri Blass

Date: 12:31:02 10/03/03

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On October 03, 2003 at 15:15:55, Anthony Cozzie wrote:

>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

The question is not definitions.

The point is that if I sacrifice a queen I may want to extend threat of mate but
not threat of winning a bishop.

I want to extend threat to get a position that is better than the position that
I already know that I have based on search.

Uri



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