Author: Rolf Tueschen
Date: 05:09:58 12/19/02
Go up one level in this thread
On December 18, 2002 at 22:55:56, Bruce Moreland wrote: >On December 18, 2002 at 22:36:27, Russell Reagan wrote: > >>On December 18, 2002 at 21:16:53, Bruce Moreland wrote: >> >>>You get into trouble when you are safe for the moment, but the computer has a >>>longer term threat that you can't escape. The short depth null-move search >>>won't detect the threat. >> >>In this case, I have to ask, will an extra two plies be able to detect that long >>term threat? If it's a long term threat, I wouldn't think it would matter >>whether you subtract two (or three) plies from the normal full width search. > >I will go into more detail. > >Let's say that your current depth is 5. You are going to make each of your >moves, and then give black a 4-ply response. > >Before you do that, you do the null move thing. What this amounts to is you >pass your move and allow your opponent a chance to search. What depth is this >search? It depends upon the depth-reduction factor (R). R is how this saves >time -- it takes advantage of the fact that moving twice is usually so potent >that you don't need a lot of search to kill your opponent if that's possible. >The typical value for R is 2. What this means is that the search that black is >going to get to do will be 2 plies, which is 4 - 2. > >So they get a 2-ply search, which is a chance to kill you, and a chance for you >to respond. After your response, they don't get a chance to kill you again, >because this is a 2-ply search not an infinity-ply search. > >Some programs cannot detect non-capturing mates at the horizon, so if this >program is like that, black could have a mate in one, and it would not be >detected. > >So the knife stops inches from white's heart, white thinks he is fine, and this >whole line is discarded as "awesome for white". > >Let's assume that we had not done the null move test. Now, for each of white's >moves, black gets a four-ply shot at white. It is possible that in every case, >black makes a threat, white cannot parry it, and black mates on the third move. >There's an extra white move left over, but white is already dead. > >So white is dead, and white will figure this out, and fail low on this >variation. > >Do you understand? If you don't, I will try again, because this is important. > >This kind of stuff happens a lot when playing against humans, who sacrifice >stuff in order to mate you. I think it's the single worst problem that you'll >have if you use traditional null move search with R=2. Yes, exactly, but therefore all such stuff is in vain. I (the super GM) play you (with disregard to my humiliated self that normally forbade me to play chess like that), bring you into a closed position, then find out where the key is hidden for the endgame and then I will bust you with a deep plan, of which you won't 1) see the end, 2) know how to prevent it technically and 3) have anything in _your_ realm to find help. So - busted. Rolf Tueschen > >bruce
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