[Bug-gnubg] Snowie and GNU wrong

[Albert Silver]

I ran across this rarity so I thought I'd share it. In game 4, move 8,
both GNU 0.14 and Snowie 4 are completely wrong. GNU agreed with
Tissona's play and Snowie said 13/9 10/9 was the only move. A rollout
showed both to be wrong.

GNU Backgammon  Position ID: g+9OABCYZ+IAFg
                 Match ID   : MAEmA0AAAAAA
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     O: Moshe Tissona
 |       O     O    |   | O     O     X    |     4 points
 |             O    |   | O     O          |     Rolled 41
 |                  |   | O                |     
 |                  |   | O                |     
 |                  |   |                  |    
^|                  |BAR|                  |     25 point match (Cube:
1)
 |                  |   | X                |    
 |                  |   | X                |     
 | O           X  X |   | X                |     
 | O           X  X |   | X        O     X |     
 | O     X     X  X |   | X        O  O  X |     0 points
 +13-14-15-16-17-18------19-20-21-22-23-24-+     X: Jon Royset

    1. Cubeful 2-ply    23/22 13/9                   Eq.:  -0.292
        45.5%   8.4%   0.1% -  54.5%  17.4%   0.4%
        2-ply cubeful 100% speed [world class]
    2. Cubeful 2-ply    13/9 10/9                    Eq.:  -0.315 (
-0.023)
        45.5%   8.7%   0.1% -  54.5%  19.1%   0.4%
        2-ply cubeful 100% speed [world class]
    3. Cubeful 2-ply    23/22 6/2*                   Eq.:  -0.329 (
-0.037)
        45.1%   9.6%   0.1% -  54.9%  20.1%   0.5%
        2-ply cubeful 100% speed [world class]
    4. Cubeful 2-ply    13/9 6/5                     Eq.:  -0.349 (
-0.057)
        48.6%  10.5%   0.1% -  51.4%  29.3%   1.6%
        2-ply cubeful 100% speed [world class]

    1. Rollout          13/9 6/5                     Eq.:  -0.262
        49.2%  10.3%   0.2% -  50.8%  27.5%   1.4% CL  -0.211 CF  -0.262
      [  0.3%   0.2%   0.0% -   0.3%   0.2%   0.1% CL   0.008 CF
0.017]
        Full cubeful rollout with var.redn.
        648 games, Mersenne Twister dice gen.
        Play: 0-ply cubeful [expert]
        Cube: 2-ply cubeful 33% speed
    2. Rollout          23/22 13/9                   Eq.:  -0.320 (
-0.058)
        44.1%   7.8%   0.3% -  55.9%  16.4%   0.3% CL  -0.211 CF  -0.320
      [  0.3%   0.2%   0.1% -   0.3%   0.2%   0.0% CL   0.007 CF
0.015]
        Full cubeful rollout with var.redn.
        648 games, Mersenne Twister dice gen.
        Play: 0-ply cubeful [expert]
        Cube: 2-ply cubeful 33% speed
    3. Rollout          23/22 6/2*                   Eq.:  -0.339 (
-0.077)
        44.6%   8.9%   0.3% -  55.4%  19.1%   0.5% CL  -0.221 CF  -0.339
      [  0.3%   0.2%   0.1% -   0.3%   0.2%   0.1% CL   0.008 CF
0.018]
        Full cubeful rollout with var.redn.
        648 games, Mersenne Twister dice gen.
        Play: 0-ply cubeful [expert]
        Cube: 2-ply cubeful 33% speed
    4. Rollout          13/9 10/9                    Eq.:  -0.354 (
-0.092)
        44.0%   8.1%   0.3% -  56.0%  18.2%   0.5% CL  -0.232 CF  -0.354
      [  0.3%   0.2%   0.0% -   0.3%   0.2%   0.1% CL   0.007 CF
0.017]
        Full cubeful rollout with var.redn.
        648 games, Mersenne Twister dice gen.
        Play: 0-ply cubeful [expert]
        Cube: 2-ply cubeful 33% speed