Author: Miguel A. Ballicora
Date: 22:39:05 02/28/01
Go up one level in this thread
On March 01, 2001 at 01:35:53, Miguel A. Ballicora wrote: >On February 28, 2001 at 16:52:05, Robert Hyatt wrote: > >>On February 28, 2001 at 14:49:19, Miguel A. Ballicora wrote: >> >>>On February 28, 2001 at 13:22:41, Robert Hyatt wrote: >>> >>>>On February 28, 2001 at 11:10:30, Miguel A. Ballicora wrote: >>>> >>>>>On February 28, 2001 at 05:56:36, Leen Ammeraal wrote: >>>>> >>>>>>I am not sure about when to avoid nullmoves. >>>>>>I omit it: >>>>>>a. when in check >>>>>>b. when there are less than 5 pieces (including pawns) on the board >>>>>>c. when the last move was a nullmove >>>>>>d. at the root node >>>>>>Should I also omit it in some other cases, >>>>>>for example, when any hashmove (even with a low draft) was found, >>>>>>or when beta = alpha + 1? >>>>>>Thanks in advance for any help. >>>>>>Leen >>>>> >>>>>Hi Leen, >>>>> >>>>>Regarding b, I do not know whether what I am doing now is correct but I think >>>>>that works for me: >>>>>When either black or white had no "long range" pieces (bishop, rook or queen) >>>>>I disable null move. The rationale is that one side cannot waste >>>>>a tempo in a given position having pawns, king and/or knights making the >>>>>position prone to have a zugswang. >>>>> >>>>>Miguel >>>> >>>> >>>>That seems dangerous. you are white, with a bishop on d5. I am black and I >>>>have a pawn on a7 and g7. The bishop is zugged here. If your king can't move, >>>>you lose even though you have a long-range slider on the board. And null move >>>>will fail high here naturally as not moving is better than having to move and >>>>lose. >>> >>>I think that you meant a3 and g3? >> >>Sorry. I am white, you are black trying to stop both of my pawns. >> >> >>> If that's so I got your point >>>and you're right. However, I disable nullmove when _either_ side lacks a >>>long-range slider. In your example, it will be disabled because you do not >>>have a bishop. If you do have a bishop, it won't be disabled (both sides got a >>>slider) but at least I don't have "mutual" zugswangs which are the nastiest (I >>>think). At least, with a slider per side the mutual zugswangs are more difficult >>>(of course not impossible but I have to draw a line somewhere). >> >> >>That only makes it worse. So I have a bishop and two pawns threatening to >>promote. You have the bishop as above. You are _still_ zugged. I don't >>see why you would limit null move based on _both_ sides. You should only >>limit it if the side on move can be zugged. But in any case, it still fails >>if we both have a bishop. > >The idea is to limit the nullmove when there is a zugswang that matters. >In other words, there are zugswangs where it does not matter if I move or not. >The example that you give could be one as pointed out by R. Gibert. If you move >you lose because you are zugswang if you don't I win anyway advancing one of the >pawns. Let me give an example trying to keep the spirit of your criticism >so I can illustrate the idea: > >[D]2k5/1p6/1K5p/2p4P/2P5/1P2b3/8/4B3 w - - 0 1 > >White plays Bg3 and Black is zugswang. Black king can move without losing a pawn >and Bishop can move defending c5 and at the same time avoiding Bf4. >This is not a mutual zugswang, because if white is on the move still win wasting I meant CAN'T... Miguel
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