Author: Robert Hyatt
Date: 18:10:27 09/29/01
Go up one level in this thread
On September 29, 2001 at 15:43:01, Uri Blass wrote: >On September 29, 2001 at 14:51:03, Robert Hyatt wrote: > >>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. > >There are always cases when null move help but the point is that there are >usually more cases when it helps when the move is 0.01 worse. > >bad captures are pruned by null move later in the tree when there is a problem >to prune good moves later in the tree. > >> >> >> >>> >>>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... > >Even if you search the best move first it is important. >In the diagram that I gave if your order of move is perfect you are going to >prune Qh4 by null move faster than you are going to prune Nc6(assuming that Nc6 >is the best move). > >you are not going to prune the ply 2...Qh4 by null move pruning because Qh4 has >a threat Qxe4+ but after Qh4 Nxh4 you are going to prune every legal move of >black by null move pruning. > >A similiar thing is not going to happen after 2...Nc6 because 2...Nc6 is not >only a move that threats something(positional threat) but you also cannot reject >a big part of the black moves as no threat after a move like 3.Bb5 >> >> >> >>>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. > >If Nxh4 is the first move that is searched by the computer after Qh4 then >I call it a killer move and I assume that Nxh4 is the first move that is >searched by good programs because it is better to start to search from a good >capture of the queen and not from a capture of a pawn. > >Maybe my definition is not correct. >I am not sure about definitions. > >Uri Captures are generally _not_ put in the killer move list. Captures are very position-specific, notably in ripping the last piece moved by the opponent when the move is stupid. Killer moves are non-captures and are generally good moves in lots of positions...
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