Author: Bruce Moreland
Date: 00:00:24 01/20/00
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On January 20, 2000 at 02:21:53, Dan Newman wrote: >On January 19, 2000 at 20:37:58, Dann Corbit wrote: > >>Under exactly what conditions does NULL move degenerate? >>Under exactly what conditions does NULL move remain valid? >> >>I see a lot of banter about the conditions of the test (when none were stated >>except depth). What conditions matter and why? > >Null-move should work at any node where passing isn't the best move. There >are two ways it can go wrong that I know of: 1) the node is one where passing >is a good move (zugzwang) and 2) the search is too shallow. There is an important case that doesn't involve zugzwang. I am tired so I'm not sure if you covered this, but in case you didn't, here it is. You are sitting in a node and D=8, so you are going to search all of the successors to D=7, if you don't do null move. Let's say that your opponent has a combination that takes 7 plies of search to see. You will find it if you don't do null move, so you will fail low. If you do null move, with R=2 you will search to D=5, with the opponent moving first. So you get <pass> and then five more plies, or 6 in total. Perhaps you really need all 7, since passing doesn't cause your position to decay. This might not allow the opponent enough time to carry out their combination, so null move finds no threat, and you fail high. So the problem here is that you get killed not by the null move, but by the depth reduction. This is a danger in any forward pruning scheme that reduces depth for some possible moves. bruce
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