Author: blass uri
Date: 11:31:13 05/14/00
Go up one level in this thread
On May 14, 2000 at 13:04:18, Heiner Marxen wrote: >On May 14, 2000 at 01:46:54, blass uri wrote: > >>On May 13, 2000 at 23:15:33, Robert Hyatt wrote: >> >>>On May 13, 2000 at 21:12:21, blass uri wrote: >>> >>>>On May 13, 2000 at 18:02:13, Robert Hyatt wrote: >>>> >>>>>On May 13, 2000 at 16:49:59, blass uri wrote: >>>>> >>>>>>On May 13, 2000 at 16:30:27, Robert Hyatt wrote: >>>>>> >>>>>>>>I understood that the idea behind chest is that it has not to try all the ply=1 >>>>>>>>moves to find that there is no mate in 2(it is obvious for mate in 1 when you >>>>>>>>need to generate only threat king moves but I understood that it is also >>>>>>>>possible to do it for mate in 2). >>>>>>>> >>>>>>>>Chest knows for every piece the squares that it controls so it knows the squares >>>>>>>>need to be controled in order to do mate. >>>>>>>> >>>>>>>>If it is obvious from the starting position of the pieces that they cannot >>>>>>>>control the relevant squares in 2 moves then you can discover that there is no >>>>>>>>mate in 2 without generating moves. >>>>>>>> >>>>>>>>Uri >>>>>>> >>>>>>> >>>>>>>what about zugzwang??? >>>>>> >>>>>>chest proves that there is a no mate without really executing the moves and it >>>>>>does not do errors in zugzwang positions. >>>>>> >>>>>>I understand that it does not assume no move for the defender but assumes a >>>>>>simple strategy(king move if possible) and try to prove that the squares cannot >>>>>>be controled in 2 moves by the attacker. >>>>>> >>>>>>Uri >>>>> >>>><snipped> >>>>>In my case, I need to know that there is a forced mate at the current position, >>>>>so that the null-move won't be tried. There are lots of zugzwang mates where >>>>>you have to confirm that no matter what you do you get mated, even if you are >>>>>not in check. And if you do nothing, you don't get mated instantly. >>>>> >>>>>I am trying to point out that (a) the test is very expensive because it has to >>>>>be done so many times >>>> >>>>I agree that the test has to be done many times but many times a small number is >>>>not very expensive if the number is small enough. >>>> >>> >>>Confucious say "if you multiply a big number times anything, you get a big >>>number." :) >>> >>>I can add a single if statement and see the NPS change. If I add it in the >>>right place... >>> >>> >>> >>> >>>>The number of times you need to do the test is exactly the number of times that >>>>you find that there is no threat and if the time that you need to discover that >>>>there is no mate in 2 is 10 times smaller than the time that you need to >>>>discover that there is no 3 ply threat then you can earn important information >>>>because you sometimes can miss mate in 2 in searching for 3 ply threats because >>>>of null move pruning or by the fact that the evaluation does not know that a >>>>position is mate. >>> >>>I don't do any "threat" detection of any kind. When I enter a new node, I try >>>a hash probe, followed by a null-move search to see if I can exit quickly. >> >>a null move search is a threat detection. >> >>What I suggest is that if the null-move search tell you that you can exit >>quickly to do a mate threat search for the same depth that is clearly faster >>than the null move search and only if the mate threat search tell you there is >>no mate threat then you can exit. >> >>Sometimes null move search to depth 3 cannot see mate in 2 so this idea can be >>productive against mate attacks. >> >>The reason that I suggest it is that I saw that Crafty has problem in detecting >>some ideas about mate attacks. >> >>Crafty lost against tal in the millenium tournament after it fell victim to mate >>attack and I saw that crafty could not see a sacrifice of chessmaster against >>Insomniac because of mate threat prunning. >> >>I posted the position when crafty needed 10 plies to see Nf5 but the problem was >>some plies early when crafty could not see the winning sacrifice of chessmaster. >> >>You can also decide to use the idea of mate search after null move search only >>in part of the positions when you can see by evaluation king safety problem so >>you will do it after sacrifices like Bxh2+ >> >>I was careful now to suggest only mate in 2 after 3 ply search but it is >>possible that mate in 3 after 3 ply search is also not a waste of a long time if >>you do it only in positions when there is a king safety problem. >> >>It is possible to stop mate attacks also by better evaluation but I do not think >>that you are going to use big evaluation in order to sacrifice a bishop for mate >>attack because of positional reasons and if you do not do it then the only way >>that I see to do something against mate attacks is by improving the search. >> >> I >>>don't do any kind of 'searching' or 'analysis' to determine if a null-move is >>>safe to try... >>> >>> >>> >>> >>>> >>>>I think that searching for mate in n by chest is usually clearly faster than >>>>searching 2n-1 plies forward by crafty. >>>> >>>>Uri >>> >>> >>>I wouldn't be surprised at all. Finding mates is far easier if you are only >>>looking for them and not trying to play a real game... But the question is >>>still how much does it cost. >>> >>>I like the relatively simple search I am using. as simple -> bug-free. Yes, >>>I wish it could do some things quicker. It will when I take the time to get >>>the singular extension stuff implemented... >> >>I do not know if singular extension will help much if you prune threat mate move >>after null move search when the search is not deep enough. >> >>Even if they help I think that my idea can also help. >> >> >>Uri > >I am very pleased that the ideas implemented in Chest stimulate such an >interesting discussion :-) > >I tend to agree with you, Uri, that a special mate threat detection can >help, if designed carefully. Some time ago I have also tried to suggest >a verification procedure for null move prunings. A mate threat search >could help some problems, which really are there, but also are not exactly >frequent, they are somewhat rare. > >Also, the methods of Chest use a comparatively big board: for every field/ >position there are maintained two attack sets, which are quite crucial for >the operation of Chest. That makes the move execution inside chest an >expensive operation, quite unlike most playing programs, including crafty. > >I tend to agree with Bob that throwing in an additional mate threat search >can easily slow things down a lot. > >Embedding the ideas for fast mate search into a playing program would need >to completely re-evaluate the ideas and to completely re-design the >implementation, IMO. That is not a small/quick mini-project. Obviously >Bob has not yet run out of ideas he considers easier to implement. >So... who volunteers to work out these things until we all see it can be >done and is quick enough? I do not volunteer :-( What about you, Uri ? > >Heiner I also do not volunteer to do it. It is of course easier to think about ideas than to write them. The reason that I suggested this idea is the fact that I did not like to see programs become victims of mate attack of tal because of the behaviour of the programmer of tal and I found that in the millenium tournament tal often won because of mate attacks. I thought that my idea could help to stop part of the mate attacks of tal(it is better to do it by evaluation but I do not see a way to know by evaluation when a sacrifice of a piece is right). I think that this idea may be important also against humans who try to win programs by mate attacks. Some mate attacks are too deep and cannot be stopped by search but some mate attacks can be stopped by search. In the Israeli league 2 programs were victims of mate attacks(Fritz and Rebel) and it seems to me that in this case the mate attack could be stopped also by search. In the last game of Fritz that was posted today the mate attack could not be stopped by search. Uri
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