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Explain XG rollout results to the not bot-savvy

Posted By: leobueno
Date: Friday, 22 August 2014, at 2:38 a.m.

In Response To: Explain XG rollout results to the not bot-savvy (leobueno)

Thanks for your suggestions. Here is what I have so far.

What do all the numbers mean? The solutions to the problems are printouts of analysis by a computer program, Xtreme Gammon (“XG”). Checker Plays For checker plays, the printouts look something like this: XGID=-BBABBBbB---c-----B-babcb-:0:0:1:32:2:1:0:5:10

1. Rollout¹ 8/3 eq:+0.486

Player: 62.36% (G:13.55% B:0.34%)

Opponent: 37.64% (G:2.88% B:0.05%)

Confidence: ±0.010 (+0.477..+0.496) - [100.0%]

Duration: 1 minute 32 seconds

2. Rollout¹ 6/4 6/3 eq:+0.373 (-0.113)

Player: 60.61% (G:10.04% B:0.15%)

Opponent: 39.39% (G:3.56% B:0.06%)

Confidence: ±0.011 (+0.362..+0.384) - [0.0%]

Duration: 1 minute 50 seconds

3. Rollout¹ . . . [list of other possible plays]

¹ 1296 Games rolled with Variance Reduction.

Moves: 3-ply, cube decisions: XG Roller

XGID=-BBABBBbB---c-----B-babcb-:0:0:1:32:2:1:0:5:10 is a code that uniquely describes the position under consideration.

Following the XG ID is a list of moves, in order of how good they are. In the example above, there are only two listed moves, but more may be included.

1. Rollout¹ 8/3 eq:+0.486 gives the best move’s equity (+0.486 in this case). Equity is explained below.

Player: 62.36% (G:13.55% B:0.34%) says that after this play the player will win 62.36% of games, will win a gammon 13.55% of the time and a backgammon 0.34%

Opponent: 37.64% (G:2.88% B:0.05%) indicates that the player’s opponent will win 62.36% of games, will win gammon 2.88% of the time and a backgammon 0.05%.

Confidence: ±0.010 (+0.477..+0.496) - [100.0%] tells how statistically significant the result is. In this case XG is 100% confident that this is the best move.

Duration is the computer time it took XG to analyze the position.

For the second and subsequent moves, XG lists the equity and the difference between the move in question and the top move.

2. Rollout¹ 6/4 6/3 eq:+0.373 (-0.113) means that this move has equity of 0.373 which is 0.113 worse than the best move, i.e., move # 1.

¹ 1296 Games rolled with Variance Reduction. Moves: 3-ply, cube decisions: XG Roller are the program’s settings used to analyze the positions.

The primary number to focus on is equity. Ignore all the other numbers for now. The higher the equity, the better the position is. If your equity is positive, you are winning. If it's negative, you are losing. If it's zero, you are neither winning nor losing. Winning a single game has equity of +1.000, and losing a single game has equity of -1.000, so the difference between winning and losing a single game is 2.000. When comparing two plays, look at the equity difference—this is the most important number. Anything above 0.030 is usually considered an error, and anything above 0.080 is considered a blunder. So, if the plays differ by 0.500, then making the inferior play is like throwing away half a game in one move; this is a humongous error. Most reasonable plays differ by significantly less than 0.500. An equity difference of 0.100 is like throwing away a tenth of a game—a big blunder. An equity difference of 0.010 represents one-one-hundredth of a full game and is basically inconsequential. Acknowledgement: This explanation is adapted from the comments posted on www.bgonline.org by: Bob Koca, David Rennie, ah_clem and AdamStocks.

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