Author: William Bryant
Date: 16:31:37 09/22/04
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On September 22, 2004 at 07:53:37, Andrew Platt wrote: On my old program running on a 500 mhz G4 laptop (in the background) using Null Move, I find mate in less than 2 seconds and a short mate in 6 Again, slow computer being used for other things. Screamer II build7 PLY NODES TIME SCORE PV ______________________________________________________________ 5/00 11818 0.117 +2.32 Qa4 d3 Kd7 Kd4 Qxc6 6/00 33903 0.358 ++ Qa4 6/01 86388 0.951 +3.66 e3 c3 Kd7 Kc4 Kxd6 dxe3 Kxe6 e2 Qxe2+ Kd4 6/06 102432 1.124 ++ Qb1 7/00 157130 1.822 +327.56 Qb1 d3 e3 d2 Kd7 c3 Qa2+ c4 Qa5+ c5 Qa8# 7/08 365340 4.056 +327.58 Kc7 d3 7/10 373395 4.150 +327.60 Qa1 d3 8/00 509216 5.860 +327.60 Qa1 d3 Qc3 e3 exd3 cxd3 Qxd3# William >Actually, more accurately a problem with null move and a position that appeared >in this week's Washington Post Chess column: > >[D] 3K4/8/2ppp3/2pkp3/2ppp3/8/4P3/3Q4 w - - 0 1 > >The main thing to do is to wait for black to commit suicide, something that null >moves are very bad at doing! The solution is to make an active waiting move that >will position the Queen directly later: > >1. Qa1 d3 2. Qc3 e3 3. exd3 cxd3 4.Qxd3# > >However, Schola does not want to get this mate. I can run it as long as I like >and it still goes for the longer mate: > >1. Kd7 d3 2. e3 c3 3. Qb3+ c4 4. Qb4 c2 5. Qxd6# > >If I disable null move it finds this very quickly. I suspect that there's a bug >in the search somewhere though I can't find it and the traces look sane. The >main problem is that the null move for Qa1 always cuts off so it retains Kd7 >which is the first move it considers. > >Has anyone else had problems with positions like these and null moves? BTW, I >have verified null move implemented but that doesn't help either. That does make >a small difference if I jump the position to 1. Qa1: It then finds the fastest >mate which the regular null move still doesn't do. I've also disabled some other >things like the hash table which sometimes get in the way for me but that didn't >change anything. > >Andy.
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