Author: José Carlos
Date: 08:15:25 07/25/03
Go up one level in this thread
On July 25, 2003 at 10:52:41, Uri Blass wrote: >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 I don't think Dann meant that, because the answer would be obvious. If you _know_ that the position is checkmate, what could be the reason for not returning checkmate?. If the reason is the qsearch is selective, then you couldn't return checkmate anywhere in the tree (nobody uses pure minimax). On the other hand, many (probably most) qsearchs don't do checks, so you don't know if you're checkmated or only checked, thus not returning checkmate. I do checks in qsearch in Anubis, but not in Averno. I'm very very happy with checks in qseach, and find it to be a big improvement in playing strength. José C.
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