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Nacbracs (explained in detail)

Posted By: Nack Ballard
Date: Friday, 16 December 2011, at 8:54 p.m.

In Response To: What is the meaning of " and = in nacbracs (Taper_Mike)

I concur with Stick's and Mike's answers.

I'll elucidate more generally. A good example will be provided by one of Neil's rollouts, originally posted here but for convenience it is copied below.

is Player 2

score: 0
pip: 158
Unlimited Game
JacobyBeaver
pip: 167
score: 0

is Player 1
XGID=-a----EaC---dE-a-c-e----B-:0:0:1:32:0:0:3:0:10
to play 32
1.Rollout124/22 13/10eq: -0.2754
Player:
Opponent:
43.40% (G:10.50% B:0.41%)
56.60% (G:15.38% B:0.70%)
Conf.: 0.0017 (-0.2771...-0.2736) - [56.0%]
Duration: 8 hours 04 minutes
2.Rollout124/21 13/11eq: -0.2756
Player:
Opponent:
43.67% (G:10.88% B:0.45%)
56.33% (G:16.00% B:0.82%)
Conf.: 0.0018 (-0.2774...-0.2738) - [41.4%]
Duration: 8 hours 14 minutes
3.Rollout124/21 6/4eq: -0.2773 (-0.0020)
Player:
Opponent:
43.93% (G:10.83% B:0.46%)
56.07% (G:16.99% B:0.92%)
Conf.: 0.0019 (-0.2792...-0.2754) - [2.5%]
Duration: 8 hours 51 minutes
4.Rollout124/22 24/21eq: -0.2789 (-0.0036)
Player:
Opponent:
43.37% (G:9.77% B:0.39%)
56.63% (G:14.84% B:0.59%)
Conf.: 0.0017 (-0.2806...-0.2772) - [0.0%]
Duration: 7 hours 44 minutes
5.Rollout213/10 6/4eq: -0.2888 (-0.0134)
Player:
Opponent:
43.54% (G:10.91% B:0.44%)
56.46% (G:16.51% B:1.10%)
Conf.: 0.0032 (-0.2920...-0.2856) - [0.0%]
Duration: 2 hours 43 minutes
6.Rollout26/1* eq: -0.2920 (-0.0167)
Player:
Opponent:
42.84% (G:11.57% B:0.38%)
57.16% (G:15.68% B:0.90%)
Conf.: 0.0032 (-0.2953...-0.2888) - [0.0%]
Duration: 2 hours 48 minutes
1 101088 Games rolled with Variance Reduction.
Dice Seed: 29794098
Moves: 3-ply, cube decisions: XG Roller

2 32400 Games rolled with Variance Reduction.
Dice Seed: 29794098
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.00.154.alpha

Six plays have been rolled out. In describing the position (instead of diagramming it) and eliminating and the less important details such as win/gammon/backgammon percentages, we might summarize the data into blue typeface as follows:

The far-side player opened by rolling 63 and played 24/18 13/10.
The near-side player replied with a roll of 32. The equities of his top six plays are listed below, with relative equities (compared to the best play) shown in parentheses:

    24/22 13/10 . .2754 (best) .....101088 trials
    24/21 13/11 . .2756 (.0002) .101088 trials
    24/21 6/4 ..... .2773 (.0020) .101088 trials
    24/22 24/21 . .2789 (.0036) .101088 trials
    13/10 6/4 ..... .2888 (.0134) ...32400 trials
    6/1* ............ .2920 (.0167) ...32400 trials

Extreme Gammon version 2. Moves: 3-ply. Cube decisions: XG Roller.

If Neil had chosen to display his rollout with three decimal places instead of four, the summary would look like this:

The far-side player opened by rolling 63 and played 24/18 13/10.
The near-side player replied with a roll of 32. The equities of his top six plays are listed below, with relative equities (compared to the best play) shown in parentheses:

    24/22 13/10 . .275 (best) ....101088 trials
    24/21 13/11 . .275 (.000) .101088 trials
    24/21 6/4 ..... .277 (.002) .101088 trials
    24/22 24/21 . .279 (.004) .101088 trials
    13/10 6/4 ..... .289 (.013) ...32400 trials
    6/1* ............ .292 (.017) ...32400 trials

Extreme Gammon version 2. Moves: 3-ply. Cube decisions: XG Roller.

Nactation and "nacbracs" (Nactation brackets) provide ways to further condense the above summary:

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