Author: Peter McKenzie
Date: 12:34:02 03/28/00
[D]3qkbr1/1b1n1p1p/4pp2/rB6/P2p1B2/5N2/1P3PPP/R2Q1RK1 b - - The above position is number 30 from the GMG2 test suite (positions from a Larsen book), and causes my program's search to explode. Node counts for Lambchop 9.50, without recapture extension: 6ply: 82K, 7ply: 193K, 8ply 1262K Node counts for Lambchop 9.50, normal version with recapture extension: 6ply: 186K, 7ply: 2997K, this is a branching factor of about 15!! Does anyone else have a similar problem with this position? I'm not exactly sure why the search explosion happens because the recapture extension fires at only about 0.7% of all nodes. I restrict it to the following conditions: - don't allow 2 recapture extensions in a row - previous move must have been a swap (eg. BxN, RxR etc) - current move must be a capture by a lesser piece, or piece being captured must be unguarded. - material balance after the current move must be between -2 pawns and +2 pawns. Note: the recapture extension extends a whole ply. Perhaps my recapture conditions aren't very good, or maybe I just have a bug... input welcome! I also hacked together a version of LambChop using partial ply. Node counts for Lambchop 9.50, using 0.75ply recapture extension: 6ply: 68K, 7ply: 159K, 8ply 1328K So maybe partial play (crafty does similar I believe) is a good solution. More testing required...
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