[Bug-gnubg] Command-line bug ?

[Massimiliano . Maini]

Hi all, this bug in in the bug-tracker on gnubg.org, but it looks
so huge to me that it's maybe worth checking if anybody is having
a look at it.

    GNU Backgammon  Position ID: GwAAYAMAAAAAAA
                    Match ID   : cAkFAAAAAAAA
    +24-23-22-21-20-19------18-17-16-15-14-13-+  O: gnubg
OOO | O  O             |   |                  |  0 points
 OO | O  O             |   |                  |
 OO |                  |   |                  |
 OO |                  |   |                  |
 OO |                  |   |                  |
    |                  |BAR|                  |v (Cube: 1)
 XX |                  |   |                  |
 XX |                  |   |                  |
 XX |                  |   |                  |
 XX | X  X             |   |                  |  Rolled 21
XXX | X  X             |   |                  |  0 points
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: MaX


A hint says :

    1. Cubeful 2-ply    2/off 1/off                  Eq.:  +0.722
        86.1%   0.0%   0.0% -  13.9%   0.0%   0.0%
        2-ply cubeful prune [world class]
    2. Cubeful 2-ply    2/1 2/off                    Eq.:  -1.000 ( -1.722)
        14.4%   0.0%   0.0% -  85.6%   0.0%   0.0%
        2-ply cubeful prune [world class]

Notice that after 2/1 2/off, player 1 will double out player 2
(hence the equity of -1.000).

Now selecting the two moves and doing a rollout we get the same result
(equities of +0.722 and -1.000) in the GUI version, but a different
result in the command-line (CLI) version : it gives equities of +0.722
and -0.713. As pointed out by the person that reported the bug (Philippe
Michel), -0.713 is the cubeless equity.

It is not a coincidence, since the same behavior appears for the following
position :

    GNU Backgammon  Position ID: GwAAYAsAAAAAAA
                    Match ID   : cAkFAAAAAAAA
    +24-23-22-21-20-19------18-17-16-15-14-13-+  O: gnubg
OOO | O  O             |   |                  |  0 points
 OO | O  O             |   |                  |
 OO |                  |   |                  |
 OO |                  |   |                  |
 OO |                  |   |                  |
    |                  |BAR|                  |v (Cube: 1)
 XX |                  |   |                  |
 XX |                  |   |                  |
 XX |                  |   |                  |
 XX | X  X             |   |                  |  Rolled 21
 XX | X  X  X          |   |                  |  0 points
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: MaX

Here, no matter the move, player 1 is gonna double out player 2 next turn.
While GUI version correctly shows equities equal to -1.000 after a rollout,
CLI version shows cubeless equities ...



(MaX) hint
    1. Cubeful 2-ply    2/off 1/off                  Eq.:  -1.000
        12.0%   0.0%   0.0% -  88.0%   0.0%   0.0%
        2-ply cubeful prune [world class]
    2. Cubeful 2-ply    3/off                        Eq.:  -1.000 ( +0.000)
        12.0%   0.0%   0.0% -  88.0%   0.0%   0.0%
        2-ply cubeful prune [world class]
    3. Cubeful 2-ply    2/1 2/off                    Eq.:  -1.000 ( +0.000)
         9.6%   0.0%   0.0% -  90.4%   0.0%   0.0%
        2-ply cubeful prune [world class]
    4. Cubeful 2-ply    3/1 2/1                      Eq.:  -1.000 ( +0.000)
         0.0%   0.0%   0.0% - 100.0%   0.0%   0.0%
        2-ply cubeful prune [world class]
(MaX) rollout =1 =2 =3 =4

    1. Rollout          2/off 1/off                  Eq.:  -0.761
        12.0%   0.0%   0.0% -  88.0%   0.0%   0.0% CL  -0.761 CF  -0.761
      [  0.0%   0.0%   0.0% -   0.0%   0.0%   0.0% CL   0.000 CF   0.000]
        Truncated cubeful rollout (depth 11) with var.redn.
        648 games, Mersenne Twister dice gen. with seed 1036242101 and
quasi-ran
dom dice
        Stop when best play is enough JSDs ahead: limit 1.96 (min. 144
games)
        Play: world class 2-ply cubeful prune [world class]
        keep the first 0 0-ply moves and up to 8 more moves within equity
0.16
        Skip pruning for 1-ply moves.
        Cube: 2-ply cubeful prune [world class]
    2. Rollout          3/off                        Eq.:  -0.761 ( +0.000)
        12.0%   0.0%   0.0% -  88.0%   0.0%   0.0% CL  -0.761 CF  -0.761
      [  0.0%   0.0%   0.0% -   0.0%   0.0%   0.0% CL   0.000 CF   0.000]
        Truncated cubeful rollout (depth 11) with var.redn.
        648 games, Mersenne Twister dice gen. with seed 1036242101 and
quasi-ran
dom dice
        Stop when best play is enough JSDs ahead: limit 1.96 (min. 144
games)
        Play: world class 2-ply cubeful prune [world class]
        keep the first 0 0-ply moves and up to 8 more moves within equity
0.16
        Skip pruning for 1-ply moves.
        Cube: 2-ply cubeful prune [world class]
    3. Rollout          2/1 2/off                    Eq.:  -0.809 ( -0.048)
         9.6%   0.0%   0.0% -  90.4%   0.0%   0.0% CL  -0.809 CF  -0.809
      [  0.0%   0.0%   0.0% -   0.0%   0.0%   0.0% CL   0.000 CF   0.000]
        Truncated cubeful rollout (depth 11) with var.redn.
        144 games, Mersenne Twister dice gen. with seed 1036242101 and
quasi-ran
dom dice
        Stop when best play is enough JSDs ahead: limit 1.96 (min. 144
games)
        Play: world class 2-ply cubeful prune [world class]
        keep the first 0 0-ply moves and up to 8 more moves within equity
0.16
        Skip pruning for 1-ply moves.
        Cube: 2-ply cubeful prune [world class]
    4. Rollout          3/1 2/1                      Eq.:  -1.000 ( -0.239)
         0.0%   0.0%   0.0% - 100.0%   0.0%   0.0% CL  -1.000 CF  -1.000
      [  0.0%   0.0%   0.0% -   0.0%   0.0%   0.0% CL   0.000 CF   0.000]
        Truncated cubeful rollout (depth 11) with var.redn.
        144 games, Mersenne Twister dice gen. with seed 1036242101 and
quasi-ran
dom dice
        Stop when best play is enough JSDs ahead: limit 1.96 (min. 144
games)
        Play: world class 2-ply cubeful prune [world class]
        keep the first 0 0-ply moves and up to 8 more moves within equity
0.16
        Skip pruning for 1-ply moves.
        Cube: 2-ply cubeful prune [world class]



Pretty scary to me ...


MaX