SF misevaluating pawn endings

[Eelco de Groot]

Joerg posted on https://github.com/official-stockfish/S ... issues/760

@Stefano80 @Kingdefender But will this also be helpful in positions with more pawns like the one mentioned above? Iam not sure, maybe I will give it a try tomorrow. It should be easy enough to try.

I rather reply here now because I think Rocky's issue gets a bit sidetracked. This is a very different position. I don't think treating KPk bitbase evals differently will help a lot here. Your suggestion for changing LMP will, but unfortunately you lose some speed I think. Stefano's suggestion is more a logical change because you make better use of exact results in the KPk bitbase. I guess, in positions where you hit KPk it should even be a little speedup because you don't need to search a draw position anymore (only in Root to get a move) but not so much that Marco will be satisfied by that. It should leave LMR intact though.

I don't know how much extra code is involved.... If your point of view is that Syzygy bases should solve this, I don't think we have much chance. I depends if it can be cleanly done?

By the way for Peer's position 1 I have an alternative suggestion that even lowers the benchnumber Old bench with Vondele's latest refactor patch:

bench: 5884767

New bench with modificated latest Development Stock:

Stockfish 20161205 MOD _02
===========================
Total time (ms) : 3112
Nodes searched : 5879059
Nodes/second : 1889157

Code: Select all

      // Step 13. Pruning at shallow depth
      if (   !rootNode
	       && !&#40;pos.count<ALL_PIECES>&#40;WHITE&#41; + pos.count<ALL_PIECES>&#40;BLACK&#41; <= 5&#41;  // New condition
	    /* && !&#40;PvNode && !pos.non_pawn_material&#40;pos.side_to_move&#40;))) */
          &&  bestValue > VALUE_MATED_IN_MAX_PLY&#41;
      &#123;

Will return always something like this


8/1p4p1/5k2/5p2/8/3K3P/5PP1/8 w - -

Engine: Stockfish 20161205 MOD _02 HT (7 threads, i7 6700, 512 MB)
by T. Romstad, M. Costalba, J. Kiiski, G. Linscott

30/55 0:01 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 f2 12.Kxf2 Kf4 13.Ke2 Ke4
14.Kf2 (28.197.992) 19857

31/55 0:01 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 f2 12.Kxf2 Kf4 13.Ke2 Ke4
14.Kf2 (33.953.160) 20114

32/55 0:01 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 f2 12.Kxf2 Kf4 13.Ke2 Ke4
14.Kf2 (40.140.731) 20222

33/55 0:02 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 f2 12.Kxf2 Kf4 13.Ke2 Ke4
14.Kf2 (57.295.204) 20706

34/55 0:03 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (80.122.010) 21286

35/55 0:05 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (113.809.223) 22407

36/55 0:09 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (234.291.665) 24842

37/55 0:10 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (253.566.325) 24964

38/55 0:12 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (304.774.696) 25387

39/55 0:19 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (516.614.250) 27164

40/55 1:34 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (2.782.650.592) 29573

41/55 4:04 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (7.373.300.745) 30140

42/55 4:09 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (7.490.207.986) 30054

43/55 4:31 0.00 1.f4 b5 2.Kd4 Ke6 3.g4 Kf7 4.Kc5 g5
5.Kxb5 gxf4 6.Kc4 fxg4 7.hxg4 Kf6
8.Kd3 Kg5 9.Ke2 Kxg4 10.Kf2 f3
11.Kf1 Kg3 12.Kg1 f2+ 13.Kf1 Kh2
14.Kxf2 (8.122.271.067) 29967