Author: Stuart Cracraft
Date: 18:11:00 08/18/01
So I've been dinkering with null move. Or it's been dinkering with me. Without using null move, an 8-ply search in the opening position looked like: ply time nodes score pv 1 0.00 21 28 d2d4 2 0.00 97 -20 d2d4 d7d5 3 0.06 842 16 d2d4 d7d5 g1f3 4 0.06 3423 -15 e2e4 g8f6 e4e5 f6e4 5 0.17 22430 1 e2e4 e7e5 g1f3 g8f6 b1c3 6 0.77 87605 0 e2e4 e7e5 g1f3 g8f6 f3e5 f6e4 7 3.90 502473 11 e2e4 e7e5 g1f3 b8c6 d2d4 e5d4 f3d4 c6d4 d1d4 8 25.27 2944173 -6 e2e4 e7e5 g1e2 g8f6 b1c3 c7c5 f2f4 b8c6 f4e5 c6e5 After null move is enabled (a few extra lines of code -- see below), all hell breaks loose with the pv after the 4th iteration. ply time nodes score pv 1 0.00 21 28 d2d4 2 0.00 97 -20 d2d4 d7d5 3 0.00 469 16 d2d4 d7d5 g1f3 4 0.06 1943 -20 d2d4 d7d5 g1f3 g8f6 5 0.11 13981 -2 c2c3 b8c6 g1f3 e7e5 d2d4 6 0.39 48418 -1 e2e3 b8c6 g1f3 d7d5 d2d4 g8f6 7 1.21 147016 20 e2e3 b8c6 g1f3 d7d6 d2d4 e7e5 c1d2 8 14.17 1598546 -9 e2e3 b8c6 d2d4 e7e5 d4d5 c6e7 g1f3 g8f6 f3e5 e7d5 I like the times and node-count but hate the variations even more (pieces en prise, etc.) The related code: : : /* No null move if any of the following is true: * at a pv node * at frontier * having made a null move in this variation * side to move's king is in check * previous move is null move * material difference between sides + pawn is still below beta * piece material of side to move less than a bishop * too deep in the tree */ if ( !pv_node && depth > 1 && !innull && !c && MATERIAL+ValueP[pawn] > beta && piece_material[side] > ValueP[bishop] && ply < 5 ) { index[ply+1] = index[ply]; nm.from = 0; MakeMove(nm); nullscore = -search(-beta, -beta+1, depth-3, 1); /* 1 -> innull */ UnMakeMove(); if (nullscore >= beta) return(nullscore); } } : : I've tried dropping a variety of the above conditions, to no avail. Anyone else see lousy pv's upon use of a null move? --Stuart
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