Author: Robert Hyatt
Date: 19:07:43 07/01/02
Go up one level in this thread
On July 01, 2002 at 18:03:21, Bas Hamstra wrote: >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. Yes I have. Why do you think early versions did checks, while the current version does not? I made this decision just before Jakarta after playing thousands of games with and without. qsearch checks see _way_ more in some positions. They see _way_ less in others. The question is, which is most important. I have voted with my "editor". :)
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