Author: Robert Hyatt
Date: 06:55:58 07/08/98
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On July 08, 1998 at 06:20:18, Inmann Werner wrote: >To make ma program faster I included Null-Move and a cutoff one ply >before the horizon, if the position is "good". >On the other hand, simple mates go beyond the horizon (also because of >small quiet search). > >My idea: > >If I do a Null-Move it Cuts if greater Beta. OK >if it is much lower than alpha I extend the search, because it could get >to some interesting mate. > >The idea behind: In Null move the other side can do 2 moves in row. If this >gets to a very high score (mate) it is interesting enough to extend. >I made some tests, and the program really found the mates 1 to 2 plys faster. >Also, the program does not get much slower. > >Is this a "good idea". Why not use Null-Move the other way round? > >Comments? > >Werner I think the idea is one that has "been tried and found wanting". It has problems for a couple of reasons: 1. many programs use PVS or Nega-scout algorithms, which means that 99.999% of all nodes searched have alpha=beta-1, making it difficult to return a value "very much lower than alpha" to trigger this. 2. once you try it for a while, you find it has simply cost you a lot of time. I don't know of anyone using this method any longer, including Chrilly... But there is one useful thing you can do... at ply N+1, you *can* return an accurate score, namely "mate". And this can be useful. Bruce was the first I know of that used this method, and it works well. If you do nothing, and you get mated, then there is obviously a "threat" in the position and it is worth searching deeper. I do this too, but *only* for mate, because I can't detect when the score is "well below alpha" because it can't happen in PVS.
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