Author: Scott Gasch
Date: 16:39:10 09/12/04
Go up one level in this thread
On September 12, 2004 at 18:19:04, Volker Böhm wrote: >Hi Scott, > >the idea behind a check-extension is not only to find great attacks beginning >with a checking move. One other major idea is to prevent horizont effects. >Example: you give away a piece for a really good attack. But the opponent has >the opportunity to give you some checks, pushing the really good attack out of >sight. Extending the checks in positions below alpha helps to fix this problem. > >I never found a good idea to reduce check extension. I always extend a checking move 1 ply. What I'm talking about is deciding to either extend or not extend the one legal response on the next ply. I agree with you about checks: I've never found a way to safely not extend them. Even if the checking side is way ahead it could be checking just to push something really bad over the horizon. >By the way why do you extend on promotion? I never heard anyone doing it. Thus >maybe the reduction will work here (the more reduction the better :-) > >A reduction that gained a little was the pawn-pushed-to-row-7 extension that I >only extend, if the pawn on row 7 cannot be taken without material loss (SEE >= >0). I wonder if the price of running the SEE on such a move is worth it. Or are you doing it with attack tables? I do the poor man's version of that -- I don't extend a pawn push if there's a piece blocking it in its new position. >Something that could be tested (I think) is the reduction of the >take-back-extension that is perhaps not that usefull if far away from the >search-window. > >On the other hand: maybe futility, extended futility and razoring is a better >concept than reducing extensions by comparing against alpha and beta. Thus I >think you should test your ideas only if you have at least futility. I have futlity in the qsearch but nothing else. The first post I made is about how if you decide to extend or not based on bounds you could run into a situation where you search with a minimal window, decide to extend, fail high, research with a full window, decide not to extend, and fail low. I think the same thing is possible with all this futility stuff people like to do: if you are deciding to prune moves or not based on alpha you can search quite a different tree on the research of a node with a full window, right? Scott
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