Author: Vincent Diepeveen
Date: 05:10:10 08/26/01
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On August 25, 2001 at 23:22:45, Pham Minh Tri wrote: I see what you mean. No i'm not using this extension and will not even try. Ed Schroeder is using a completely different type of search than mine, so it makes no sense IMHO to try it. I'm using a depth limited search with nullmove R=3 and no other forms of forward pruning. Not even futility i'm using in qsearch. Best regards, Vincent >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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