Author: Owen Lyne
Date: 08:34:27 04/17/00
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On April 17, 2000 at 10:42:33, William Bryant wrote: >On April 16, 2000 at 09:53:15, Robert Hyatt wrote: > > >>Crafty stops at the right point, _unless_ given a sd=N command. It uses the >>rule of "search to 2*N=1" when it finds a mate in N, just to be sure there >>isn't a shorter mate. In the position you gave, it stopped after 4 plies >>as that is the minimum depth it will normally search to, regardless of the >>mate found... >> > >I'm not sure I understand you rule to exit a search with a mate score. > >Do you search to 2 times the depth of the mate, ie 4 ply for a mate in 2? I think Bob made a typo, I think he meant (2*N -1), ie mate in 1, depth 1, mate in 2, depth 3, mate in 3, depth 5 etc This is the number of ply to the mate, so certainly you don't need to search beyond that. However stopping at ply 4 when you have a mate in 4 say would be wrong, because there could be a mate in 3, which you won't spot till ply 5. Null move and other pruning can mean some mates take a while to see, while other mates, with more checking moves for example, may be see via extensions earlier than expect. Hence a mate in 4 found at ply 4, a mate in 3 found only at ply 5, you probably want to keep searching till that mate in 3, not exit on finding the mate in 4. Owen
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