Author: Uri Blass
Date: 10:13:10 07/04/02
Go up one level in this thread
On July 02, 2002 at 14:20:30, Bas Hamstra wrote: >On July 01, 2002 at 22:07:43, Robert Hyatt wrote: > >>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". :) > >I have done many experiments too and it certainly works for me. But (as I once >read in another thread) you want to do checks everywhere and totally OR not at >all. IMO that's not the way to do it. According to MANY experiments I did, it >works best if you limit qchecks to the first 1 or 2 plies. It solves the >nullmove "blindness" for mates almost entirely. For me it costs 0,5 ply nominal >searchdepth. But this loss in depth is merely optical, because in selfplay (at >least in Blitz) the qcheck version wins with BIG margins. What do you mean by big margins? 60%,65% or 70%. How many games did you play? Can you give exact results of your experiment? Thank in advance Uri
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