Author: Robert Hyatt
Date: 08:29:46 04/27/04
Go up one level in this thread
On April 27, 2004 at 00:59:32, rasjid chan wrote: >On April 26, 2004 at 16:13:52, Robert Hyatt wrote: > >>On April 26, 2004 at 15:56:13, Sune Fischer wrote: >> >>>On April 26, 2004 at 15:02:23, Robert Hyatt wrote: >>> >>>>On April 26, 2004 at 14:25:01, Sune Fischer wrote: >>>> >>>>> >>>>>>(1) you are in some sort of zugzwang position where a null-move will fail high >>>>>>for the wrong reason and wreck the search. Classic examples here are positions >>>>>>with very few pieces. IE pawns vs a knight where the knight can be zugged. >>>>>>Most require some minimal amount of material on the board to avoid this problem. >>>>>> >>>>>>(2) there is a tactical issue that is hidden with the R reduction. IE the >>>>>>classic position with white pawns at f2, g3 and h2, black queen at h3 and black >>>>>>pawn or bishop at f3, threatening mate on the move. If the R reduction prevents >>>>>>you from seeing the mate, you can have problems. >>>>>> >>>>>>(3) The hash table proves that the null-move search will not fail high, meaning >>>>>>that the search will be wasted effort. >>>>>> >>>>>>(4) Obvious positions such as when the side on move is in check. Not moving >>>>>>can't fail high here as the king is lost. >>>>>> >>>>>>(5) I don't allow two consecutive nulls. It is a potentially cute way of >>>>>>eliminating zugzwang problems, but it is only good for that, and it is not free >>>>>>in positions where no zugzwang is possible. I choose to not deal with it >>>>>>although I have this on my "to do" list to test with (say) pawn-only endings. >>>>> >>>>>The first 4 I agree with, unfortunately 1 and 2 are not so easy to detect. :) >>>>> >>>>>I don't get the point of (5) though, how does it avoid zugzwangs? >>>> >>>>Think about it this way. >>>> >>>>You do a null move search. If you are in zugzwang, it will fail high for the >>>>wrong reason, since doing nothing in a zugzwang position is a good thing. Agree >>>>so far? >>> >>>Yes. >>> >>>>What we are hoping to show is that our position is so good, even if we do >>>>nothing our opponent is busted. IE We are a queen up, and the most valuable >>>>piece our opponent attacks is a knight. If we don't try to save the knight we >>>>are _still_ winning. >>> >>>Yes >>> >>>>Now, take the bad null-move case where we are in zugzwang. The null search >>>>fails high for the wrong reason. But if, at the next ply, you try a null it >>>>will _also_ fail high, causing that side to return beta, which makes _our_ null >>>>search fail low and not kill us in the zugzwang position. >>> >>>Exactly, you want the nullmove to FL when you are in zugzwang, so >>>I don't see how this is an argument in _favor_ of (5)? >> >>Maybe we are semantically dancing around the head of the pin? >> >>IE I don't do 2 nulls in a row as in most middlegame positions zugzwang is not >>an issue and the second (of two consecutive nulls) is wasted effort. I have >>plans to experiment with turning this double-null on in endgames however, as >>there zugzwang is _very_ common and the detection would seem to be a >>more-than-break-even deal. > >When sugzwang is not an issue, then infinite n-th consecutive nullmove >seems optimal, or is this dumb? > >The premise is our criterions for nullmove are valid and reliable >otherwise we should not be doing even one nullmove. I'm not sure I follow. Null-move is most effective when one side is winning by a significant margin, such as where a move at a shallow ply drops a queen, and deep into the search nothing has been won back. The side that is winning tries a null and it works. The side that is losing will never get a fail-high on a null... >By induction, the more nullmove the greater the savings and advantage. >The conditions for the 2nd/n-th nullmove is the same as the one before >and do not depend on what goes before if we assume uniform criterion >quality,that it is cheaper then a full-width search. Note that there is no restriction on the number of null-moves that can be played along any single path, just that there can never be _two_ consecutuve null moves. All I can say is that I have tried it both ways and in the middle-game, two consecutive nulls made the tree somewhat larger. I haven't re-tested in several years however... > >So maybe the findings of nullmove everywhere, and maybe add all-the-time, >may be correct. > >Rasjid > > > > >> >>IE I am not saying double null is always bad. Just that it is bad in the >>middlegame and as a result I don't do double-null anywhere at the moment... >> >> >>> >>>>>I don't see any logical reason to do (5), because after you have nullmoved you >>>>>want to see if the other side can FH so we may FL on the nullmove. The fastest >>>>>way to do that is to do another nullmove. >>>> >>>>In normal positions, if I am a queen up, and I try a null, if you also try a >>>>null you are _still_ a queen down, the null-search fails low, and you continue >>>>to search normally making that second consecutive null-search wasted effort. >>> >>>In this case his nullmove will FL so you waste a cheap nullmove to depth X-2R. >>>On the other hand, suppose his nullmove fails high, then you have saved a full >>>search to depth X-R! >> >>Yes, but in the middlegame you almost _always_ waste that X-2R search. In >>today's 14-16 ply (plus extensions to make it even worse) that is a non-trivial >>wasted effort. In endgames it will likely pay off... >> >>> >>>It seems logical that if a nullmove is worth while (statisticly) at depth X, it >>>should also be worth while (statisticly) at depth X-R. >> >>No, for one reason. If the depth=X search is done, in a reasonable place, the >>X-R search will fail low and be wasted effort. If you can't guarantee that the >>X-R search is going to pay off fairly frequently, then doing it just burns >>search space. In the endgame this is different since zugzwang is a big part of >>such positions... >> >> >> >> >> >>> >>>Assuming of course we have no game specific knowledge of en prised or pinnes >>>pieces or anything like that. >>> >>>It's like you're hoping so much that your first nullmove will FH that you don't >>>even want to try a quick check to see if it might actually FL :) >> >>All I really care about is fail highs on zugzwang positions. Fail lows are not >>an issue... >> >> >> >> >>> >>>>>So I get the same results as Tord here, it's weaker (slightly, but measurably) >>>>>with this restriction on. >>>>> >>>> >>>>As I said, YMMV... >>> >>>Oh of course, as always! :) >>> >>>-S.
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