Author: leonid
Date: 04:20:59 03/29/00
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On March 28, 2000 at 15:34:02, Peter McKenzie wrote: >[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... Don't use in my game any extensions (only special logic search for mate) but maybe these data could be useful. Tried on LLchess, AMD 400Mhz. Brute force search. WHITE do 6 ply search in 0.549 sec. 8 ply search 23 sec. Average number of nodes in each ply is 37. Average number of nodes per ply that logic search for 7 and 8 ply is 6.5 nodes. Average number of nodes searched in one second 192648. BLACK do 6 ply search in 0.549 sec. 8 ply search 40 sec. (39.7sec). Average number of nodes per ply is 34. Average number of nodes per ply that logic is forced to search is 8.5 nodes. Average number of nodes serched in one second is 224588. Leonid.
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