Author: Vincent Diepeveen
Date: 05:10:36 12/15/99
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On December 15, 1999 at 08:08:53, Ulrich Tuerke wrote: >On December 15, 1999 at 06:59:46, Steve Maughan wrote: > >>I was analysing a position with my program when I came across the following: >> >>rkb2r2/1p2R1pp/1pp5/2P5/2B5/P7/1P1Q1PPP/n2K4 w - - 0 1 >> >>There is nothing special about the position apart from the search path that >>resulted. I use a 'one good reply to check' extension. Good meaning 'move that >>does not obviously give away material'. Now I had thought that this was a >>relatively well-behaved heuristic that allows some deep mates to be found in >>lightening time. However the search path that resulted was as follows: >> >>1. Qd6+ Ka7 2. cxb6+ Kxb6 3. Qb4+ Ka7 4. Qa5+ Kb8 5. Qe5+ Ka7 6. Qc5+ Kb8 7. >>Qd6+ Ka7 8. Qd4+ c5 9. Qxc5+ Kb8 10. Qd6+ Ka7 11. Qd4+ Kb8 12. Qe5+ Ka7 13. Qe3+ >>Kb8 14. Qg3+ Rf4 15. Qxf4+ Ka7 16. Qe3+ Kb8 17. Qe5+ Ka7 18. Qa5+ Kb8 19. Qc7+ >>Ka7 20. Qc5+ Kb8 21. Qd6+ Ka7 22. Qa6+ Kb8 > >I just cut lines like this, i.e. lines where one and the same piece keeps on >checking without capture moves. My search will return zero evaluation in this >case because this could probably be perpetual check. Of course, this is sort of >risky. Very risky. i experimented with exactly the same. my program played a lot better without it. Of course it scored less at a few testsets. >Uli > >> >>IMO this is 44 ply of wasted search. One of the insights I have had while >>writing this program is that it is easy to come up with sensible extensions that >>work in some positions, but it is difficult to come up with good extensions that >>cut-off quickly when not relevant. >> >>The question is - is there a way of taming the above heuristic that will cut off >>the search earlier, but will still retain the advantages of being able to find >>deep mates? >> >>My ideas so far are: >> >>1) Cut-off after a given depth. >>2) Store the path of the king and only allows the search to continue if the king >>moves to a new square. >>3) Only allow one occurrence of attack-square and king-square. >>4) Only allow the search to continue if there have been captures in the last 'n' >>moves. >>5) Combination of 1 and 4. >> >>Remember that these heuristics would only be relevant for the 'one reply to >>check' heuristic. >> >>I haven't yet tries all of the above ideas but the classic position that would >>be spoilt by most of them is the 'mate in 30': >> >>5n2/B3K3/2p2Np1/4k3/7P/3bN1P1/2Prn1P1/1q6 w - - 0 1 >> >>Hmmm - any ideas? Has anyone managed to tame the extension? What do others do? >> >>All help, comments and suggestions appreciated! >> >>Steve Maughan
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