Author: Roberto Waldteufel
Date: 15:49:39 07/11/98
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On July 11, 1998 at 13:44:32, Bruce Moreland wrote: > >On July 11, 1998 at 11:45:25, blass uri wrote: > >>I am interested in positions only one program can solve >> >>Vincent Diepeveen posted on June 29 the following 2 positions >>r4rk1/pp1n1p1p/1nqP2p1/2b1P1B1/4NQ2/1B3P2/PP2K2P/2R5 w - - bm >> >>the solution is Rxc5 and diep found the move after 6:42 >>and found the advamtage for white after 13:14 >>he used 60MB hash tables >>and I think he used pentium200MMX >>my programs found only Bf6 with draw. > >I thought I posted something about this last week. > >Mine finds this in two minutes on a P2/300. The score it gets isn't great, it's >a little negative. Other versions have found this quickly with scores of +2 or >more. > >>can another program solve this position in 1 hour? >> >>the second position: >>r1b2rk1/1p1nbppp/pq1p4/3B4/P2NP3/2N1p3/1PP3PP/R2Q1R1K w - - bm Rxf7 >>diep found the move after 22 minutes and 43 seconds > >This one takes four minutes to get a slight positive score, five minutes is +1. > >I like the Nolot positions, I've been fiddling with them for a few years. If >you want to see more from me, look for "Nolot" in the "old" archives in r.g.c.c, >or perhaps even just rec.games.chess. > >I can get solutions in some of the other Nolot positions as well. > >>can another program find this move in 1 hour? >> >>(according to Robert hyatt deep thought solved the position after 2 minutes but >>I cannot buy deep thought so it is not important for me) >> >>in Rebel's homepage there is mate in 30 Rebel can find(all the moves of the >>loser are forced). >> >>can another chess program find the mate? > >I can't find it, feel free to post it. > >Long mates are often the result of positions where one side is in check and has >only one legal way out. > >One very old extension in computer chess involves extending when you make a move >that gives check. > >If you also extend on the reply, when there is only one way out, you get the >checking move and the reply without decreasing depth at all. > >If there is a long forcing sequence you can find mates in very large numbers of >moves in just a few nodes. This has been well-known for years. > >It is hard to find long mates that don't involve this extension. > >bruce Hi Bruce, I never reduce the depth when the side to move is in check, but I find that if I do the same for moves that administer check it sometimes blows my search sky high, hanging the machine for an inordinate amount of time. It's a pity, because I also found many times that this method discovered long mates as you describe. How do you overcome the problem of situations where the number of checks becomes excessive, eg a king being chased around the board by a queen that lacks supporting pawns or pieces to deliver a mate? Best wishes, Roberto
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