Author: Ed Schröder
Date: 23:32:31 05/18/99
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>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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