Author: Bas Hamstra
Date: 15:03:21 07/01/02
Go up one level in this thread
On June 30, 2002 at 12:26:25, Robert Hyatt wrote: >On June 29, 2002 at 00:57:05, Peter McKenzie wrote: > >>On June 28, 2002 at 23:31:11, Robert Hyatt wrote: >> >>>On June 28, 2002 at 16:33:10, Scott Gasch wrote: >>> >>>>I've been experimenting with checks in the qsearch. While implementing this I >>>>ran across a couple of old posts from Bob who said, in essence: If side to move >>>>is in check in the qsearch but has had a chance to stand pat at a previous ply >>>>in the qsearch then the check is not forced and generating all replies to check >>>>is wasted nodes. >>>> >>>>I am struggling with this idea. If you are in check and have no good way out >>>>your opponent will fail high and you will just stand pat where you could at a >>>>previous ply. I get that. So is the idea to only generate responses to check >>>>that have a chance at not failing low? Maybe only capturing responses and >>>>blocking or king flees? Imagine you are in check and have no capture responses >>>>so you conclude there is no good way out of check -- is it sound to return -MATE >>>>to force your side to stand pat where it could have at a previous ply? I >>>>suppose the assumption here is that if you are in check and way below alpha >>>>running away or blocking the check is not going to do the trick and you will end >>>>up standing pat at a previous ply anyway. >>> >>>Here is the problem. It is my move. I can stand pat. Or I can make a >>>capture. If I make a capture, you check me and now I have to get out of >>>check and am mated. You back up a mate score and I will refuse to make this >>>capture and just stand pat. So you can't _prove_ that every move leads to >> >>Sure, and thats just fine. Your unsound capture is refuted, just as it should >>be. Therefore the score backed up will be more accurate. > >Wrong. The q-search is _full_ of errors. Assuming a capture is best when >the opponent might have an impossibly strong threat move you don't look at >and so you don't see it. > > >> >>>a mate, because whenever I get to stand pat, I stop the mate right there. >>> >>>The only way to fix this is to follow checks if and only if every move for >> >>Fix what? I don't see anything that is broken. > > > >Fix the fact that you are causing your q-search to explode badly, where most >of the time the search space you add does _nothing_. It doesn't refute a >capture, you just look at checks that are captures and make the other side >look at all possible moves to be sure it isn't mated. > >I'm not about to say it isn't a good thing. I do say that in lots of testing >I decided that if I was going to follow checks, I was going to maintain the >ability to recognize forced mates as a result. Evading check after _any_ >capture in the q-search is highly expensive... and will cost a ply easily >in some positions, more in wildly tactical positions. Without letting you >find deeper mates at all. Have you ever self-played a qcheck version of Crafty versus a normal one? Just try it. It sees WAY more. Nullmove is simply inaccurate without it. Bas.
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