Author: Robert Hyatt
Date: 13:03:13 06/26/03
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On June 26, 2003 at 08:11:23, Albert Bertilsson wrote: >Hi Everybody! > >Previously I've used check-extensions, and now I added single-reply extensions. >This has given me some problems because it seems that the engine tries to extend >to much now! Some positions are just searched to very few plies. I guess it has >to do with one side only having one move to do (single-reply) and the other side >constantly checking, and this makes the search go deep immediatly and not >returning until searching to max depth or getting 3-fold repetition. > >I've solved this temporarily by only allowing to extend at most Depth plies, so >when searching to ply 6 maximum search depth should be 12 plies. Anybody have a >better idea? > >Forgive me for interrupting the other threads with this computer chess related >question. This is still the computer chess forum? > >/Regards Albert One danger is the number of extensions you allow. IE if any ply can extend by a whole ply, it is _possible_ that you get a non-terminating search. But in reality, this is not likely since to extend at ply=N, you do a check, and it is unlikely that at ply=N+1 you also do a check extend. But of course, if you do one-reply extension, then you have the potential for a problem since you could get into the non-terminating condition. It is more common, however, to have multiple extensions at one ply, and there you have to be careful. If you extend by 2 plies at any ply, then even though you might not extend at the _next_ ply you are already ahead of the game and are on the way to a non-terminating condition. fractional extensions are a good way to limit this. IE I extend 1 ply for checking the opponent, and 3/4 ply for the one-reply-out-of-check. Since a search has to go a full ply, a 3/4 ply extension doesn't extend unless another fractional extension is added, either at this ply or at one farther down in the tree. Just remember the danger point is 1 ply of extension per ply is a killer. Or two plies of extensions for every two plies. If you don't stay below that limit, you can see a 1 ply search take forever.
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