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Subject: Re: not using nullmove? [generalized null move]

Author: Dann Corbit

Date: 22:05:46 02/13/04

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I think the interesting thing about null move is that it is easy to figure out
if a move is really bad -- which is the main reason why it causes a benefit.  A
tempo advantage is easily calculated by just switching sides.

But the idea can be generalized nicely.

Suppose that you have a seven ply search performed and it is time to do an 8 ply
search.  Suppose (further) that from the root node only you never analyze the
root itself but instead analyze all of the child nodes of the root and save the
values.

Now, you have some sort of estimate for the "goodness" of each move. Things
might get reversed on the next ply, but it isn't terribly likely.  After all, we
look at crappy moves and search them less deeply with the null move heuristic.

Now, suppose that we have 10 moves available:

move 0 has an evaluation of +100 centipawns
move 1 has an evaluation of +80 centipawns
move 2 has an evaluation of +77 centipawns
move 3 has an evaluation of +60 centipawns
move 4 has an evaluation of +53 centipawns
move 5 has an evaluation of +19 centipawns
move 6 has an evaluation of +5 centipawns
move 7 has an evaluation of -10 centipawns
move 8 has an evaluation of -110 centipawns
move 9 has an evaluation of -910 centipawns

Will we (knowing this) want to search them all the same?

Why not use a logarithmic scale based on the difference between the best
possible move and the move under consideration?

Another advantage:
Zugzwang sorts itself out.

We can also add refinements like increasing the shear with mobility increase
(greater reductions if I have 90 choices than if I have 12).

Using estimates from a database also works nicely.  Unfortunately, hash table
estimates have not worked out well for me (for attempts using other than the
root).



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