Author: Robert Hyatt
Date: 11:00:15 01/29/02
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On January 29, 2002 at 12:21:56, James Swafford wrote: >On January 29, 2002 at 09:53:21, Robert Hyatt wrote: > >>On January 28, 2002 at 23:20:45, James Swafford wrote: >> >>> >>>Does anybody do this? I just implemented a passed pawn extension >>>that extends the depth by 1 if the move was a pawn move to the >>>sixth or seventh rank, and that pawn is not blocked by a pawn of >>>the opposite color. >>> >>>The results are pretty disappointing. It really blew up my search. >>>I decided to modify the implementation by saying only looking for >>>pawn pushes to the seventh rank, and it still can blow up pretty >>>bad. >>> >>>Obviously most over the board positions would not trigger this >>>extension, but there are some that would blow up the search like >>>mad. >>> >>>One thought I had is to use a fractional extension scheme. That >>>may help, but I'd like to know if anybody else does this extension, >>>and what mechanisms they have in place to keep the search bloat >>>under control. >>> >>>It's interesting to note that Bruce lists five different extensions >>>on his (excellent) web page; he hasn't actually written about any of >>>them yet, but passed pawn isn't even listed. Hmm... >>> >>>Any ideas or comments? >>> >>>-- >>>James >> >> >>I extend 3/4 ply when a passer reaches the 7th. But that only happens on the >>ply where it is pushed to the 7th... > >I knew you did fractional ply extensions from some time back. >How do you deal with the fraction once all extensions have been >added up? For example, if you end up with extensions totalling >1.75 ply, do you truncate or round? Truncate, sort of. When I do a 1 ply search, I start "depth" at 1.50... so that the first two .75 ply extensions will "trigger" a deeper search: 1.5 + .75 = 2.25, truncated to 2... 2.25 + .75 = 3.00, which is 3 plies. But 3.00 + .75 is still 3.00 so the third fractional extension doesn't trigger. But the next three will thanks to that .75 "head-start" just added in by the extension that didn't make it go deeper... Basically this says that 3 of every 4 3/4 ply extensions will really make us go deeper, which helps to control the tree explosions...
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