Author: KarinsDad
Date: 12:37:49 08/05/99
Go up one level in this thread
On August 05, 1999 at 14:36:00, Robert Hyatt wrote: [snip] >> >>I believe you either misinterpreted what I wrote or I wrote it really lousy. >> >>If you have mate in 220, you could search side positions (which contain a pawn >>push or a capture within the tablebase) as you continue making moves. >> >>Move 1: Don't bother to search for side position. >>Move 2: Search for side position that have mate in 219 (you do not really need >>to do this here, but read on), if successful, you have defered your mate in 220 >>to mate in 219, but you have reset the 50 move counter. >>. > > >the problem here might be that if you move a pawn at move X, the next >possible pawn move might well be more than 50 moves beyond X. But at >X you "committed" and now you draw. You have to search all the way to >the end and find a PV that doesn't have a 50-move draw or three-fold >repetition in it, before you enter into that line. And that is just too >far to search, not to mention the fact that all this stuff is on disk and >is very slow to access.. Yes, this could happen. But who cares? If you are in a mate in 220 half moves, you are looking at a draw anyway due to the 50 move rule. If you then move 60 half moves and then find a mate in 180 half moves nearby and that mate does not have any other way out to do this again, you will draw. You are a perfectionist Robert. You do not want the program to commit to move that could lead to a draw. I am not. I know the program is already in a draw, so I will commit to an action that may win or may draw. >>. >>. >>Move 87: Have to mate, push, or capture within 12 moves or you draw. Say you >>find a side position with mate in 150. You are currently at mate in 133. From >>where you were 86 moves ago, you can reset your 50 move counter and drop the >>mate in 220 with 99 moves to make until a draw, to mate in 150 with 99 moves to >>make until a draw. If you can get one more major drop like this (due to a >>capture or a push), you can mate your opponent. >> > >that will work in some cases, and break in others. Because when you make >an 'irreversible' move, you can't take it back, and it might commit you to >a path that has an unforseen 50-move draw that now you can't avoid. Because >you didn't follow the complete path... That's the entire point. You do not CARE if it breaks. If it succeeds, then you mate. If it fails, then you draw. But you were going to draw ANYWAY (assuming you are playing against another program with tablebases). > >>I think it would be EXTREMELY easy to find a capture or a push nearby which >>maintains a win in a LOT of positions. This does not mean that it will be easy >>to do this at any given ply. But sooner or later, it should be easy to do after >>doing an 8 ply search 50 times over (for some positions). > >the question is "lot" = "most" or just "some"? This has to be tested, and >at present, we don't have many endings where this is an issue (IE Eugene's >KBNKN was one example that just barely has the problem). We need a position >with a pawn to really see how this works out... If the answer is 1% of the time on 1% of games (due to it being rare in the first place that you will get in a mate in 100+ situation), then it would seem that it would be worth doing (after doing a lot of other things in a program first which give you more bang for the buck). Yes, I agree. Research has to be done to see how much this will buy you. But, it will always buy you something IF there are any positions out there where this will work (which I have to believe is the case). >> >>Of course you cannot do a 220 ply search. But the point is that you do not have >>to. You only have to find a push or capture that leads to a position that >>maintains the win. > >But you can't verify this without the 220 ply search. Because what happens >after you make that push/capture must allow a path without a 50-move draw in >it, but you won't know if you don't search far enough to see it before you >make the push now. If I am in a mate in 150 position (I was previously in a mate in 200) and I find a mate in 170 that resets the counter, then I do not care if the mate in 170 does not have another pawn push or capture in it. I am destined to draw in the mate in 150, so I take the chance. The worse that can happen to me in the mate in 170 position is that I draw due to the 50 move rule. > >> >>Granted, there could be weird fortress positions or somesuch where this would >>not work (as per your information on Lewis Stiller's work below). But as a >>general rule, it will probably work at least occasionally. And, it is more >>likely to work in a position where the side to win has one or more pawns. And, >>it does not matter if it doesn't work for a given position. That position is >>drawn anyway. The fact is that it probably will work for SOME positions and that >>is the reason to do it (i.e. if it preserves 10% of wins in these rare cases >>where the win is beyond 99 ply, then that is a good enough reason to do it). >>Note: you do have to make sure the program has no timing bugs so that it never >>loses on time attempting this and this includes the time it takes to read other >>tablebases in from the hard drive. >> > > >Against humans this doesn't matter. I've never seen anyone play any sort >of tablebase position against crafty in anywhere near an optimal manner. > >IE the KNN vs KP ending I saw was a mate in 103, but it went from 103 to maybe >80, to 55, to 30 over 5 moves, because the human didn't play it very well. If >you are playing a computer with tablebases, it will be different, of course, >as since it always goes for the deepest mate (if losing) that will tend to make >it follow lines with potential 50 move draws in them... Agreed. > >>> >>>>Anyway, my basic point is that you would not HAVE to search far. Sooner or >>>>later, you would most likely find a win preserving move within 6 or 8 ply >>>>(depending on how much time you have and how far you can search the tablebase) >>> >>>Lewis Stiller disproved this. He found lots of positions where a playable pawn >>>move (or capture) happened more than 70 full moves from the original position. >>> >>>It would be absolutely impossible to search 140 plies in a 6 piece ending. It >>>would be impossible to search even 60 plies in most of them unless they are all >>>pawns and they are locked up totally... >>> >> >>I am not familiar with Lewis Stiller's work. I have not yet read his Berkeley >>talk or his thesis (but I plan to now). >> >>However, the question comes down to whether or not positions in the graph close >>to the PV of the tablebase (within 8 ply for example) can reset the counter. >>From what you have stated here, I am not convinced that this cannot happen. > > >Sure it can. But it also may commit you to a course of action that is bad, >because if you push _here_ you don't have that pawn push to save you later. >The only way to resolve this is to search to the mate position making sure >you don't cross over the 50 move rule problem anywhere along the way... But it is ONLY bad in that it draws instead of drawing. What is bad in that? It was already drawn due to the 50 move rule. If the opponent makes a mistake, it probably doesn't matter which mate in x variation you are in, the mate in x will drop to mate in y where y < x. If the oppoent does not make a mistake, you at least have a CHANCE to find another push or capture that will eventually get you below the 99 moves. There is nothing to lose and only something to gain. Since you only do this when you know you are originally in a mate in 99+ - number of moves since last capture or push, you only have to worry about it when your game if effectively drawn with perfect play anyway. KarinsDad :) >Your >>example of 70 full moves does force one to conclude that there are 6 piece >>positions where this cannot be done and a draw is forced. However, if this is >>truly the case, then it does not matter. There is NO win preserving move within >>50 full moves that can be used for that position, so it does not matter there. >> >>Nothing you have said convinces me that this technique cannot maintain a win in >>at least some percentage of those rare cases where one side has mate in 100+. >>How often this will do this is debatable without more data. >> >>KarinsDad :)
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