Author: David Blackman
Date: 00:02:51 11/24/98
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On November 23, 1998 at 09:20:43, Robert Hyatt wrote: >It's not as bad as it sounds, because remember that I said to search the *other* >moves to D-2. If the fail high search costs you X nodes, then the extra tests >on the moves you would normally look at will only cost you w/w^(D=2) nodes >which lets you constrain the cost quite a bit. It certainly isn't free, but >it doesn't double the size of the tree or anything close to that... > >ie if your normal branching factor (W) is 36, then the tree will grow by a >factor of about 1/36... not too bad.. Are you sure about that? Given that you're still using alpha-beta i'd have thought the cost of checking the extra moves was about w * w^((D-2)/2) compared to finding the initial fail high at w^(D/2) ie, about the same. Although i could be missing something due to failing high and failing low having different costs. Certainly, when i attempted singular-move extensions a few years back i found that detecting singular moves was often more expensive than doing the extension. However i only did a one-ply extension. I think Deep Blue does a 2 ply extension in most cases. I briefly considered always doing the extension, without checking if it was singular, but then i decided that was silly. I guess you could reduce the cost of detecting singular moves a bit by cutting 3 or more plies off the depth, instead of just 2. I think i tried that at one stage. It's nice for tactical problem sets, but not clear if it actually helps in real games.
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