Author: Christophe Theron
Date: 23:13:14 05/30/99
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On May 31, 1999 at 00:57:00, eric guttenberg wrote:
>Cristophe,
>
>Can you explain then why F5.32 will solve the problem immediately when
>the position is set up in infinite analysis rather player v Fritz?
>
>eric
I don't know exactly what's in Fritz, but I not very surprised that something
like that happens.
Explaining you why is a very difficult task if you don't have strong knowledge
of computer chess programming.
Null move is used together with the alphabeta algorithm. Alpha and beta are two
values used during the search algorithm. Alpha is meant to be less than the
actual score of the best move, beta is a value that is above the best score.
Alpha and beta are used (amongst other things) to decide when to do a null move
search, and when the result of null move search says that you can ignore the
rest of the line.
Normally, the alphabeta search is only able to say which is the best move. You
have no idea of what move is the second best and so on.
In order to find the second best move you have to play with the values of alpha
and beta and start the search again. In this case, the null move algorithm is
going to prune away different parts of the tree (because alpha and beta are not
the same as in the first search), and there is a chance that something that was
overlooked in the first search is found in the second one.
That's why Fritz finds different things when in normal mode and when he has to
show the first best moves (Paulo Soares said that Fritz as found the move in
infinite mode with TWO OR MORE VARIANTS).
I'm not sure it's very clear, but believe me: Fritz behaviour is NOT a bug. It's
only a side effect of the alphabeta algorithm together with the use of the null
move algorithm.
I don't know why I'm spending so much time trying to explain this. Frans should
come here and explain it himself. You know, Fritz will be a tough opponent for
my program Tiger in the next World Championship! :)
Please direct any further question to Bob: first he explains this very well, and
second he likes to answer! :)
Christophe
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