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interests / rec.games.backgammon / A lucky guess

A lucky guess

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Subject: A lucky guess
From: pepste...@gmail.com (peps...@gmail.com)
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by: peps...@gmail.com - Sat, 27 Jan 2024 10:56 UTC

Here, there are only two candidate plays but I had no real idea
whether to go greedy or safe.
I guessed right but it really was a guess.
In fact during the review, I was expecting to be penalised.
There is a fair amount of equity at stake here with the wrong
play losing 0.04.
Wouldn't it be good if there was an expert reader of this forum
who knows about the issues here and who could explain to me
how to make the decision reliably rather than guessing?

Since I'm mathematically oriented, I wonder if there's someone
here who has a particular interest in mathematical games
(of which backgammon could be said to be one) and who has
contributed to journals of combinatorial game theory.?

Paul

XGID=aBBCCBB-----b--b-b-cb-c---:2:-1:1:53:3:2:0:11:10

X:Daniel O:XG Roller+
Score is X:3 O:2 11 pt.(s) match.
+13-14-15-16-17-18------19-20-21-22-23-24-+
| O O | | O O O | +---+
| O O | | O O O | | 4 |
| | | O O | +---+
| | | |
| | | |
| |BAR| |
| | O | |
| | | |
| | | X X |
| O | | X X X X X X |
| O | | X X X X X X |
+12-11-10--9--8--7-------6--5--4--3--2--1-+
Pip count X: 49 O: 124 X-O: 3-2/11
Cube: 4, O own cube
X to play 53

1. 4-ply 6/3 6/1 eq:+1.476
Player: 98.16% (G:57.60% B:0.06%)
Opponent: 1.84% (G:0.00% B:0.00%)

2. 4-ply 5/2 5/Off eq:+1.432 (-0.043)
Player: 95.68% (G:59.99% B:0.08%)
Opponent: 4.32% (G:0.00% B:0.00%)

3. 1-ply 6/1 3/Off eq:+0.932 (-0.543)
Player: 79.65% (G:52.69% B:0.17%)
Opponent: 20.35% (G:0.00% B:0.00%)

4. 1-ply 5/Off 3/Off eq:+0.913 (-0.563)
Player: 78.55% (G:53.96% B:0.25%)
Opponent: 21.45% (G:0.00% B:0.00%)

5. 1-ply 6/1 4/1 eq:+0.800 (-0.675)
Player: 76.83% (G:46.14% B:0.08%)
Opponent: 23.17% (G:0.00% B:0.00%)

eXtreme Gammon Version: 2.10, MET: Kazaross XG2

Re: A lucky guess

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From: tchow12...@yahoo.com (Timothy Chow)
Newsgroups: rec.games.backgammon
Subject: Re: A lucky guess
Date: Sat, 27 Jan 2024 08:37:04 -0500
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by: Timothy Chow - Sat, 27 Jan 2024 13:37 UTC

On 1/27/2024 5:56 AM, peps...@gmail.com wrote:
> Here, there are only two candidate plays but I had no real idea
> whether to go greedy or safe.
> I guessed right but it really was a guess.

I think that if you have one checker closed out, then the only time
you would clear the 5pt instead of the 6pt with 5x is if x=1 and
you don't have a spare on the 4pt, as in the position below.

XGID=aBBDBBB-----b--b-b-cb-c---:2:-1:1:51:0:0:0:0:10

Score is X:0 O:0. Unlimited Game
+13-14-15-16-17-18------19-20-21-22-23-24-+
| O O | | O O O | +---+
| O O | | O O O | | 4 |
| | | O O | +---+
| | | |
| | | |
| |BAR| |
| | O | |
| | | X |
| | | X |
| O | | X X X X X X |
| O | | X X X X X X |
+12-11-10--9--8--7-------6--5--4--3--2--1-+
Pip count X: 48 O: 124 X-O: 0-0
Cube: 4, O own cube
X to play 51

1. XG Roller++ 5/4 5/Off eq:+1.473
Player: 95.65% (G:57.49% B:0.05%)
Opponent: 4.35% (G:0.00% B:0.00%)

2. XG Roller++ 6/5 6/1 eq:+1.460 (-0.013)
Player: 96.08% (G:55.19% B:0.03%)
Opponent: 3.92% (G:0.00% B:0.00%)

eXtreme Gammon Version: 2.19.211.pre-release

At gammon go, you can occasionally find a position where it's a bit
better to clear the 5pt.

XGID=aBBCCBB------b-b-b-cb-c---:0:0:1:53:0:1:1:2:10

Score is X:0 O:1 2 pt.(s) match.
+13-14-15-16-17-18------19-20-21-22-23-24-+
| O O O | | O O O |
| O O O | | O O O |
| | | O O |
| | | |
| | | |
| |BAR| |
| | O | |
| | | |
| | | X X |
| | | X X X X X X |
| | | X X X X X X |
+12-11-10--9--8--7-------6--5--4--3--2--1-+
Pip count X: 49 O: 122 X-O: 0-1/2 Crawford
Cube: 1
X to play 53

1. Rollout¹ 5/2 5/Off eq:+1.956
Player: 95.33% (G:52.47% B:0.39%)
Opponent: 4.67% (G:0.00% B:0.00%)
Confidence: ±0.003 (+1.953..+1.959) - [99.9%]

2. Rollout¹ 6/3 6/1 eq:+1.950 (-0.006)
Player: 98.11% (G:49.37% B:0.25%)
Opponent: 1.89% (G:0.00% B:0.00%)
Confidence: ±0.003 (+1.947..+1.953) - [0.1%]

¹ 2592 Games rolled with Variance Reduction.
Dice Seed: 271828
Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.19.211.pre-release, MET: Kazaross XG2

---
Tim Chow

Re: A lucky guess

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Subject: Re: A lucky guess
From: pepste...@gmail.com (peps...@gmail.com)
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by: peps...@gmail.com - Sat, 27 Jan 2024 16:13 UTC

On Saturday, January 27, 2024 at 1:37:06 PM UTC, Timothy Chow wrote:
> On 1/27/2024 5:56 AM, peps...@gmail.com wrote:
> > Here, there are only two candidate plays but I had no real idea
> > whether to go greedy or safe.
> > I guessed right but it really was a guess.
> I think that if you have one checker closed out, then the only time
> you would clear the 5pt instead of the 6pt with 5x is if x=1 and
> you don't have a spare on the 4pt, as in the position below.
>
>
> XGID=aBBDBBB-----b--b-b-cb-c---:2:-1:1:51:0:0:0:0:10
>
> Score is X:0 O:0. Unlimited Game
> +13-14-15-16-17-18------19-20-21-22-23-24-+
> | O O | | O O O | +---+
> | O O | | O O O | | 4 |
> | | | O O | +---+
> | | | |
> | | | |
> | |BAR| |
> | | O | |
> | | | X |
> | | | X |
> | O | | X X X X X X |
> | O | | X X X X X X |
> +12-11-10--9--8--7-------6--5--4--3--2--1-+
> Pip count X: 48 O: 124 X-O: 0-0
> Cube: 4, O own cube
> X to play 51
>
> 1. XG Roller++ 5/4 5/Off eq:+1.473
> Player: 95.65% (G:57.49% B:0.05%)
> Opponent: 4.35% (G:0.00% B:0.00%)
>
> 2. XG Roller++ 6/5 6/1 eq:+1.460 (-0.013)
> Player: 96.08% (G:55.19% B:0.03%)
> Opponent: 3.92% (G:0.00% B:0.00%)
>
> eXtreme Gammon Version: 2.19.211.pre-release
>
>
> At gammon go, you can occasionally find a position where it's a bit
> better to clear the 5pt.
>
>
> XGID=aBBCCBB------b-b-b-cb-c---:0:0:1:53:0:1:1:2:10
>
> Score is X:0 O:1 2 pt.(s) match.
> +13-14-15-16-17-18------19-20-21-22-23-24-+
> | O O O | | O O O |
> | O O O | | O O O |
> | | | O O |
> | | | |
> | | | |
> | |BAR| |
> | | O | |
> | | | |
> | | | X X |
> | | | X X X X X X |
> | | | X X X X X X |
> +12-11-10--9--8--7-------6--5--4--3--2--1-+
> Pip count X: 49 O: 122 X-O: 0-1/2 Crawford
> Cube: 1
> X to play 53
>
> 1. Rollout¹ 5/2 5/Off eq:+1.956
> Player: 95.33% (G:52.47% B:0.39%)
> Opponent: 4.67% (G:0.00% B:0.00%)
> Confidence: ±0.003 (+1.953..+1.959) - [99.9%]
>
> 2. Rollout¹ 6/3 6/1 eq:+1.950 (-0.006)
> Player: 98.11% (G:49.37% B:0.25%)
> Opponent: 1.89% (G:0.00% B:0.00%)
> Confidence: ±0.003 (+1.947..+1.953) - [0.1%]
>
> ¹ 2592 Games rolled with Variance Reduction.
> Dice Seed: 271828
> Moves: 3-ply, cube decisions: XG Roller
>
> eXtreme Gammon Version: 2.19.211.pre-release, MET: Kazaross XG2
>
> ---
> Tim Chow

Thanks, Tim.
Presumably the closer the gammon percentage is to 50, the better the greedy plays are.
Here, it's a significant error to play greedy even though the gammon percentage is
uncannily close to 50/50.
So yes, it must be rare -- I didn't know that.
It's quite common to give yourself a positional weakness to increase your gammon count
but maybe not this way.

Paul

Subject	Author
A lucky guess	peps...@gmail.com
Re: A lucky guess	Timothy Chow
Re: A lucky guess	peps...@gmail.com