Author: Peter McKenzie
Date: 21:57:05 06/28/02
Go up one level in this thread
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. >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. >the side has been a check since q-search started. This means the side >getting checked _never_ has a chance to stand pat (I assume you can't stand >pat when evading a check) so that a mate is really forced and can't be >hidden by a stand pat... > > > > >> >>Another idea that I read from was that generating non-capturing checks in the >>qsearch against a side that has had a chance to stand pat already is a waste. I >>really don't understand this idea and disagree with it. Imagine black has had >>an oppertunity to stand pat but instead plays RxN (N appears hung). Well this >>looks really good unless white then generates Qd4+ forking blacks R and K and >>winning the R. If you neglect to generate checks on a side who has already had >>the chance to stand pat you let him get away with RxN and like it. If the only >>reason to add checks to the qsearch is to find mates then I agree -- checking >>after a side could stand pat is wasted. But if the goal is to improve tactical >>play then I think this idea is not sound. >> >>Scott > > >Try it and see what happens to the size of your tree. _then_ make the >decision whether the slight gain in tactical accuracy of refuting a capture >that fails to a check is worth the loss of a ply or so of overall depth >because your q-search explodes...
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