Author: Daniel Shawul
Date: 02:55:27 10/27/05
Go up one level in this thread
On October 26, 2005 at 20:21:48, Ryan B. wrote:
>Would this be a replacement for Mate Threat extension? It seems to me that it
No,this is in addition to it. BM extension is usually constrained to last few
plies of the tree, and when the score returned from null move is less than
alpha by a margin (say 200). No one extends all threats that null move returns.
most do *mate* threats, and some do other threats by constraining them a lot. It
is a nice way to increase your tactical strength. But their benefit is very
questionable overall as they hurt search depth.
Even the good old mate threat extension is not working for me right now ;)
daniel
>would extend a lot of lines that are already extended and maybe some that have
>been reduced. I do think this could help detect badly trapped pieces at the end
>of a search. Now I wish I could remember my logic when I decided it was a good
>idea to reduce some lines this would likely extend.
>
>Ryan
>
>On October 26, 2005 at 14:15:08, Tord Romstad wrote:
>
>>On October 26, 2005 at 13:10:45, Maurizio Monge wrote:
>>
>>>Hi,
>>>I have found that 2 engines ("TRACE"
>>>and "Petir") use this extension.
>>
>>SmarThink and Gothmog use them, too. The extension was
>>introduced by Sergei Markoff (author of SmarThink), and was
>>apparently inspired by some idea in an old paper of Botvinnik.
>>Sergei modestly named the extension "pseudo-Botvinnik
>>extension". I implemented them in Gothmog, noticed a
>>small, but clear improvement, and introduced the more
>>attractive name "Botvinnik-Markoff extension". :-)
>>
>>>Does anyone know what it is?
>>
>>Extending when the null move is refuted by the same move,
>>or by the capture of the same piece, two times in a row
>>(i.e. at ply N and at ply N+2). The point is to avoid horizon
>>effect problems, for instance when there is an unavoidable
>>mate or an unstoppable passed pawn, but the defending
>>side can postpone disaster for a few moves by delivering
>>checks.
>>
>>Tord
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