Author: Robert Hyatt
Date: 20:02:00 08/05/99
Go up one level in this thread
On August 05, 1999 at 15:37:49, KarinsDad wrote: >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. > that isn't the case I am looking at. I have a position that is a mate in 220 plies, or 110 moves. If I play it 'perfectly' I will make only one pawn move at move 90, but I will draw because at move 50 no pawn pushes have been played. In this position, I can push a pawn at ply=20, but if I do so, I won't be able to push it again until ply=130. And that is 10 plies too deep and again I draw if I push it at 20. But if I wait to ply 40 to push it, I can still push it again at ply=130, and now I am 'home free' with no chance of a draw, although the total mate is probably going to be much longer than 220 plies, since I had to avoid the optimal path to avoid the 50-move draws... That is the problem I don't see a way to solve, ever... >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. the same thing happens if you just play the optimal move. If your opponent is carbon-based, he will definitely make mistakes that shorten the mate. If it is silicon, it will play perfectly and force you into a draw anyway... > >>>. >>>. >>>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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