Author: Uri Blass
Date: 07:52:41 07/25/03
Go up one level in this thread
On July 25, 2003 at 10:31:20, José Carlos wrote: >On July 25, 2003 at 08:10:47, Uri Blass wrote: > >>On July 25, 2003 at 04:34:35, Amir Ban wrote: >> >>>On July 25, 2003 at 02:41:22, Dann Corbit wrote: >>> >>>>Now, a qsearch ending in checkmate may or may not really be a checkmate. After >>>>all, we only tried certain moves and it could very well be that the checkmate >>>>could be avoided. >>>> >>>>So, the burning question is... >>>>What should we do when the qsearch ends in a mate? >>>>There are lots of alternatives, from the primitive "return a mate" to "send a >>>>danger signal up the tree and let the regular search deal with it" to >>>>"extending" to... >>>> >>>>What is your favorite choice and why? >>> >>>I don't see where opinion comes in. In a node where all legal moves are not >>>considered static eval is the minimum. >>> >>>Amir >> >>I think that it is not so simple. >> >>Suppose you find in the qsearch that all captures are losing because of >>checkmate. > > You miss the point. It's not that all captures lead to checkmate, it's that >you don't detect checkmates. There are programs that detect checkmate in the qsearch. Particularly, Amir was talking about a position >with no captures out of check. If you don't try all legal moves, you don't know >if you're checkmated. I assume in this discussion that the program knows that it is checkmated in a leaf position. Movei knows for a leaf position if it is a checkmate or not a checkmate. You can assume it if you want, but I don't think that the >probability of capturing the checking piece, or capturing something to go out of >check, is bigger than 0.50 for all in-check positions, thus you're gonna make >more than 50% mistakes. > > José C. I was not talking about a situation when the king is in check and I think that Dann also was not talking about it because he talked about checkmate. I will explain it by a diagram suppose the following position is a position when qsearch is called [D]r3qrk1/5p1p/7Q/5B2/8/4P3/R4PPP/6K1 b - - 0 1 You analyze Rxa2 Qxh7# What is the value that you return from qsearch. You can return the evaluation of the root and you can be more passimistic because you detect checkmate in the search. I think that Dann meant to this in the original post because he said in the original post "Now, a qsearch ending in checkmate may or may not really be a checkmate." He did not say "Now, a qsearch ending in check may or may not really be a checkmate." Uri
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