Author: Ulrich Tuerke
Date: 05:36:26 12/15/99
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On December 15, 1999 at 08:10:36, Vincent Diepeveen wrote: >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. You're right. To be sincere, I have a couple of pre-conditions which must be fulfilled in order to apply the cut (e.g. I do not do this when attacked king's position is very unsafe). BTW, Vincent, I hope that we will meet in Paderborn again ? Uli > > >>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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