Author: Robert Hyatt
Date: 14:17:38 09/08/04
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On September 08, 2004 at 16:49:33, zaid magi wrote: >taken from: http://members.home.nl/matador/chess840.htm#EXTENSIONS >[quote] >The check extension in REBEL is rewarded in MakeMove(); when it is recognized >that the side to move moves out of check, the depth is extended with 1 ply, the >common procedure in most chess programs. > >An exception is made for the first check, it is not extended, also the fourth >check is extended with 2 plies being in sync again with common procedure to >extend every out_of_check situation with one ply. The idea behind: when there is >only one check in the tree, it is probably not so important, thus skip it. >However when you have 4 checks in the Search, the chance is big that checks play >an important role, better get in sync, thus extend 2 plies. > >Skipping the "first check" is very time sensitive, it speed-up REBEL with 25%, >however its elo gain is very small in comparison with the common procedure to >extend every out_of_check situation, for REBEL the gain is about +5 elo, you >must find out yourself if the idea works in your own engine. >[/quote] > >what does "first check" actually mean ?? >does he mean the first check that appear in that chess tree ?! >or the first check in the plies previous to the position under analysis ?!?! > >thanks for any explanation :D Means the "first check" in any path of moves. One way to do this is through fractional plies, which is the main reason I started using this idea about 20 years ago. For example, the one-reply-to-check extension can be made to skip the first such extension by just using 3/4 of a ply. Adding 3/4 of a ply doesn't extend, but if you get another one-reply extension in the same path, now you have extended 1.5 plies which adds 1 ply of depth. Alternatively you can do as I do and start every search at x.75 plies. IE my 5 ply search starts with a depth of 5.75 plies, but that only searches to 5 plies normally. Any 3/4 ply extension will take that to 6.5 which is the same as 6 plies. Another 3/4 ply extension will take that to 7.25 which extends another real ply. Another 3.4 ply extension takes us to 8, another real extension. But another only takes us to 8.75 which doesn't change the depth. IE using 3/4 ply extensions means you are really saying "extend 3 times and then skip one, which is one way of controlling tree growth. Different extensions can interact using this approach, so that one says extend for 3/4 plies, another says extend for 1/2 ply, the net result is a 1 ply extension... tidy and easy to write.
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