Author: Robert Hyatt
Date: 11:51:03 09/29/01
Go up one level in this thread
On September 29, 2001 at 11:11:33, Uri Blass wrote: > >In most cases when the moves is 0.01 worse there is a threat so you cannot prune >it by null move. That is simply wrong. Even if the second best move is only .01 worse than the first, there are zillions of branches in that sub-tree that the null-move will _still_ prune away quite nicely. Most captures, for example, are totally hopeless. Yet the search tries them all. And null-move dismisses them far faster than a normal search would. > >if you have an obvious blunder you may prune a lot by null move(maybe not in the >first ply but later) The tree is _full_ of horrendous blunders. Because _every_ move is searched at every other ply. At every other ply you will _definitely_ search a bunch of blunders, and null-move will dismiss 'em... >if the opponent capture the queen in the first ply after the blunder you can >reject a lot of moves later because they have no threat. > > Because a full-width search still looks at lots of >>very stupid moves that null-move dismisses more quickly than a normal search >>would. >> >>Null-move works just fine on the _PV_ search in fact, for this very reason. >> >> >>>Another reason: when the move is 0.01 worse the order of the moves is often >>>worse than the order of the moves after a blunder. >>> >> >> >>I don't follow. On a move scored at .01, there are _still_ zillions of blunders >>in the tree for that move. > >Yes, but these lines are often pruned quickly by the null move pruning and there >are more important lines when you do not reject them for the right reason. > The only reason you don't reject them quickly is your move ordering is broken and is not producing the right move first. As I said before, I can mathematically _prove_ that if you search the best move first, it doesn't matter whatsoever about the second-best move scores... they don't add to the size of the tree at all... >example:the position after 1.e4 e5 2.Nf3 >[D]rnbqkbnr/pppp1ppp/8/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 0 1 > >suppose 2...Nf6 is best with a difference of 0.01 pawn relative to 2...Nc6 > >I believe that there is a good probability that the killer move for 2...Nc6 does >not work in the next ply and you need to look for another killer move. > >You can be more sure that the killer move for Qh4(Nxh4) or Qg5(Nxg5) >or even a6(Nxe5) is the right move. > >Uri That's the point. But in that case, it is very likely that the same killer will work. Nxh4 isn't a killer. It is found as a winning capture and won't disturb the good killer.
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