Author: Ed Schröder
Date: 00:50:52 10/04/99
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>Subject: Re: Raw speed of Rebel 10 higher that Hiacrs 7.32 ? >>The keyword to understand the topic = extensions. >> >>Chess programs do use all kind of extensions and all chess programs do >>it another way. Some programs do not emphasize on extensions other >>programs heavily use extensions. >> >>A common example of an extension is to extend the ply-depth with "1" in >>case the king is in check. Thus instead of searching 6 ply the remaining >>tree is searched for 7 plies. If there is another king-in-check case found >>the search is extended to 8 plies and so on. >> >>So you see a 6-ply search isn't a 6-ply search as a lot of variations in the >>tree are searched deeper. >> >>Some program will extend king-in-check cases even more. On some types >>of checking moves Rebel will extend 2 plies. Other programs have their >>own ways of doing things. The end result is that you can't compare programs >>based on ply-depth. >> >>Ed > >This explanation puzzle me. My impression was that "brute force" in given >number of plys deep should include nothing but number of plys asked. Every >other extra ply for every other extra reason is inappropriate. I can only >understand that in all games logic should go some extra plys (or extention) >if it like to do this but not when "brute force" is asked. To see >some extra ply in "brute force" search (even partially) is pious fraud. It >sound >like find the mate in 5 moves but announce it as mate in four. >Brute force search in certain number of plys signify for me search for all >the possiblities that existe for given position but going only the number >of plys said to be performed. If "brute force" is what I see it to be, it says >more that every other aspect of the game about the general capability of the >chess game itself. > >Leonid. It is much worse than you think. 5n2/B3K3/2p2Np1/4k3/7P/3bN1P1/2Prn1P1/1q6 w - - bm e3g4; Try this position. Rebel will find the mate-in-30 on the second ply. Nowadays programs are not going to do a 60 ply search. They extend such cases. Ed
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