Author: Pham Minh Tri
Date: 20:22:45 08/25/01
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On August 25, 2001 at 22:29:22, Vincent Diepeveen wrote: >On August 25, 2001 at 21:49:02, Pham Minh Tri wrote: > >>Hi all, >>I have just implemented the extension "remaining": increase 1/4 depth if both >>current and previous moves are from hash. This idea I learn from Ed (and read >>about it from collection of Dann - see the post "Crafty will never win a title" >>on August 23). So far some my tests show that it is no effect - but the search >>tree explodes slightly (5-10%). Does anyone have better result? >>Pham > >Sorry i missed the extension idea, could you explain a bit more clearly? > >: what does your extension extend now and under which conditions? > >so if at iteration n, n+1 , n+2 a move m is from the hashtable then >you now extend it by 1/4 ply? > >Best regards, >Vincent I check and extend 1/4 (trying 1/2) ply if current move (computing) is from hastable and the move of the last ply (ply-1) is also from it. I re-quote the Ed post from Dann's Collection as following. He explained clearly about his idea. I just ignore currently the promotion extension: ED--> =========================================================================== Subject: Re: Q. about Rebel extensions From: Ed Schröder E-mail: rebchess@xs4all.nl Message Number: 52186 Date: May 19, 1999 at 02:32:31 In Reply to: Q. about Rebel extensions Message ID: 52090 Posted by: Rémi Coulom At: Remi.Coulom@imag.fr On: May 18, 1999 at 03:56:14 >Posted by Rémi Coulom on May 18, 1999 at 03:56:14: >>Extensions (checks) : 77.979 (13%) >>Extensions (captures) : 5.807 (1%) >>Extensions (king safety) : 1.180 (0%) >>Extensions (on depth) : 7.594 (1%) >>Extensions (remaining) : 1.094 (0%) >>Extensions (total) : 93.654 (16%) >> > >Could you explain what "king safety", "on depth" and "remaining" extensions >consist in ? Extensions (King Safety): when one of the kings is in danger an extra ply is taken. Extensions (on depth): on depth means the ply before Q-Search. Various extensions (extra plies) are tried to avoid a horizon effect. To name a few: #1 if the last move attacks 2 pieces. #2 if the king is in check. #3 if the last move is capture that gains material (static evaluation). #4 cases like bba2 wrb3 wrf7 #5 piece attacks like h2-h3 attacking the black knight on g4. #6 moves that escape from (#5) such as Nf6, Nh6, Ne5 #7 certain types of mate threats recognized by the evaluation function. All of this is safe-guarded with several forward prune techniques to avoid the tree to explode. Next, extensions on depth is limited to take 2 or 3 of such extra plies also to avoid the tree to explode. Extensions (remaining): A number of the list of "Extensions on depth" is also tried in the tree. Here I use fractional increments of 1/4 ply. One idea is to push the hash table entries of best lines. In other words, if the current move is from the hash table and the move of the previous ply too then the depth is increased with 1/4 ply. Also some promotion extensions are tried which increment may vary on their importance. Ed Schroder
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