Author: Robert Hyatt
Date: 20:31:11 06/28/02
Go up one level in this thread
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 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 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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