Author: blass uri
Date: 18:12:21 05/13/00
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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. 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 think that searching for mate in n by chest is usually clearly faster than searching 2n-1 plies forward by crafty. Uri
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