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Subject: Can nullmoves behave like this?

Author: Severi Salminen

Date: 05:16:44 01/08/01


Hi!

This position from a Kramnik-Leko game was posted recently here by Eduard
Nemeth. I tried it with my program and found odd behaviour. (See below)

[D]2br1r2/1pR1Rp2/1p3k2/1B1p1Pp1/PP1P2P1/K7/8/8 w - -

This is the output of my engine if null moves are disabled (you won't see
end-of-ply statistics except at the end of search. A info line is printed when
PV changes):
--------------------------
  Time   Depth    Score       Nodes PV
  0.00     1       0.39           7 a5
  0.00     1       0.53           9 Bf1
  0.00     1       0.59          11 Be2
  0.00     1       0.63          13 Bd3
  0.00     1       0.66          25 Re5
  0.00     2       0.53          68 Re5 Rh8
  0.00     3       0.58         233 Re5 Rh8 Kb3
  0.00     3       0.60        1065 Kb2 Rd6 Re5
  0.00     3       0.61        1256 Kb3 Rd6 Re5
  0.06     4       0.58        1694 Kb3 Rd6 Be8 Rd8
  0.17     5       0.68        7665 Kb3 Kg7 Kc3 Rd6 Re5
  0.44     6       0.56       28541 Kb3 Kg7 Re5 Rh8 Bd3 Rd6
  2.37     7       0.66      149581 Kb3 Kg7 Kc2 Kf6 Kd3 Rd6 Re5
 11.10     8       1.16      672797 Kb3
                   (++)
 14.72     8       1.29      858649 Kb3 Kg7 Bd7 Bxd7 Rxd7 Rxd7 Rxd7 b5
 44.88     9       1.29     2557418 Kb3 Kg7 Bd7 Bxd7 Rxd7 Rxd7 Rxd7 b5 Rxd5

Eval:  1.29, nodes: 3007933, qnodes: 4116797, time: 117.60, nps: 81456
Futile moves: 12023153, order:  99.0%
------------

And this is with null moves:
-----------
  Time   Depth    Score       Nodes PV
  0.00     1       0.39           7 a5
  0.00     1       0.53           9 Bf1
  0.00     1       0.59          11 Be2
  0.00     1       0.63          13 Bd3
  0.00     1       0.66          25 Re5
  0.00     2       0.53          69 Re5 Rh8
  0.00     3       0.58         277 Re5 Rh8 Kb3
  0.05     3       0.60        1149 Kb2 Rd6 Re5
  0.05     3       0.61        1358 Kb3 Rd6 Re5
  0.05     4       0.48        1662 Kb3 Rd6 Re5 Rh8
  0.22     5       0.65        7311 Kb3 Rd6 Kc2 Kg7 Re5
  0.38     6       0.58       18869 Kb3 Rd6 Re3 Rd8 Re5 Rh8
  0.99     7       0.66       65854 Kb3 Kg7 Kc2 Kf6 Kd3 Rd6 Re5
  2.19     8       1.16      156746 Kb3
                   (++)
  2.80     8       1.29      210619 Kb3 Kg7 Bd7 Bxd7 Rxd7 Rxd7 Rxd7 b5
                   (--)
  5.65     9       1.29      456674 Kb3 Kg7 Bd7 Bxd7 Rxd7 Rxd7 Rxd7 b5 Rxd5

Eval:  1.29, nodes: 199941, qnodes: 301868, time: 6.15, nps: 81594
Futile moves: 498682, order:  94.7%
-------

So both versions fail high at d=8 trying Kb3, but why does the null move version
fail low at d=9 but research with infinite window results the same score? The
PVs (and scores) are the same so I think everything is working right. Is this
kind of behaviour "normal" when using null moves or do I have a bug? Can
aspiration search and null moves cause these articats?

Severi




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