A marginal race

[peps...@gmail.com]

Obviously, this should be treated as a race but I've learned not to Axelise
these positions. The Axelisation algo has been trained only on pure
races not near-races, so I don't think the Axelisations are reliable here.
It turns out to be extremely close exactly marginal. So far, XG agrees
with my take, but that can easily change if I roll it out.
Since I chose not to Axelise, I looked at 10% + 2 and also 8/9/12.
Both give a 1-pip drop but I've learned by experience that these tend
to underestimate the underdog in this type of long-distance near-race
so I adjusted to a take. As it's so marginal, dropping would have been
just as good.

Paul


XGID=-----CD-D---cD--acad-a--b-:0:0:-1:00:4:6:3:0:10
X:eXtremeGammon O:Daniel

Score is X:6 O:4. Unlimited Game, Jacoby Beaver
+13-14-15-16-17-18------19-20-21-22-23-24-+
| X O | | O O |
| X O | | O O |
| X O | | O O |
| O | | O |
| | | |
| |BAR| |
| | | |
| O | | X |
| O X | | X |
| O 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: 109 O: 123 X-O: 6-4
Cube: 1
X on roll, cube action

Analyzed in 4-ply
Player Winning Chances: 78.67% (G:0.03% B:0.00%)
Opponent Winning Chances: 21.33% (G:0.00% B:0.00%)

Cubeless Equities: No Double=+0.574, Double=+1.147

Cubeful Equities:
No double: +0.880 (-0.117)
Double/Take: +0.997
Double/Pass: +1.000 (+0.003)

Best Cube action: Double / Take

eXtreme Gammon Version: 2.10

[Timothy Chow]

On 9/13/2022 4:39 PM, peps...@gmail.com wrote:
> Obviously, this should be treated as a race but I've learned not to Axelise
> these positions. The Axelisation algo has been trained only on pure
> races not near-races, so I don't think the Axelisations are reliable here.
> It turns out to be extremely close exactly marginal. So far, XG agrees
> with my take, but that can easily change if I roll it out.
> Since I chose not to Axelise, I looked at 10% + 2 and also 8/9/12.
> Both give a 1-pip drop but I've learned by experience that these tend
> to underestimate the underdog in this type of long-distance near-race
> so I adjusted to a take. As it's so marginal, dropping would have been
> just as good.

Another thing to be aware of is that even though this sort of position
looks very simple, it's one where XG 3-ply routinely makes mistakes.
I commented on this phenomenon back in 2013.

http://www.bgonline.org/forums/webbbs_config.pl?read=136252

For this reason, when I roll out races or near-races, I usually use the
strongest rollout settings that I have the patience for.

---
Tim Chow

[peps...@gmail.com]

I didn't have the patience to wait to the end of the rollout when I did it last night.
However, looking at the numbers, the results were remarkably similar to the
analysis stat. It consistently wobbled in the 0.99 -- 1.008 range.

Paul

[Stick Rice]

It's not just that 3 ply makes mistakes, it's that the move filter is also not large enough to handle the many legal options (esp w/smaller rolls) that comes with such positions. In this position for example I'm sure you did a standard 3ply/XGR rollout (or whatever the default is) and determined good enough, it's borderline right? Well I did a rollout with ++/++ and a gigantic move filter and the position is worth about +0.915 aka a monster take.

Stick

[peps...@gmail.com]

Your understanding of what I did is exactly correct (unfortunately). I think Tim would have approached the question more thoroughly and scientifically.
I also agree that 0.915 can be described as a "monster take".
This accords with my understanding of backgammon. For these long pseudo-races, 8/9/12 and 10% + 2 generally underrate the taker's chances quite significantly, so you have to do
a considerable adjustment, not just the one pip deficit here. That's why I took somewhat confidently OTB, and was (a bit) surprised about the (wrong) marginal verdict.

Very helpful post (by you) here!!

Thanks.

BTW, my post which (jokingly) referred to you, was an observation of mine on how weak players lose money to pros or semi-pros.
Of course, I have no idea if it applies to you personally. It's perfectly plausible (to me) that you only ever play strong players at backgammon,
and all of them know that you shouldn't always cash positions even when you have significant losing sequences.

Paul

[peps...@gmail.com]

I think Axelisation finds a big take too, despite my scepticism about using it for non-pure races.
The taker has 12 crossovers against the opponent's 11 so add 1 to the taker.
Both sides have a gap on 4,5,6 which is filled in by the opponent.
So add 1 to both.
We then get 125 against 110. 110 * 7/6 - 125 = 3 1/3 > 2 -- monster take indeed!

Paul

[Timothy Chow]

On 9/14/2022 5:55 PM, Stick Rice wrote:

> Well I did a rollout with ++/++ and a gigantic move filter and the
position is worth about +0.915 aka a monster take.

Wait, what position are we talking about? I just did an
XGR+/XGR+/Gigantic rollout and it came out to a borderline
pass. See below.

I should mention that I just bought a new laptop and installed
version 2.19.211.pre-release, which is not the version I've been
using for the past few years, but I doubt that makes a difference.
I did notice, however, that when I copied and pasted the position,
it mangled the XGID in the same way that I've seen Paul's XGIDs
mangled, and I had to correct it manually.

XGID=-B--A-DACA--dC---d-dc-----:0:0:1:00:0:0:3:0:10
X:Player 2 O:Player 1

Score is X:0 O:0. Unlimited Game, Jacoby Beaver

+13-14-15-16-17-18------19-20-21-22-23-24-+
| X O | | O O |
| X O | | O O |
| X O | | O O |
| O | | O |
| | | |
| |BAR| |
| | | |
| O | | X |
| O X | | X |
| O 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: 109 O: 123 X-O: 0-0

Cube: 1
X on roll, cube action

Analyzed in Rollout
No double
Player Winning Chances: 78.63% (G:0.01% B:0.00%)
Opponent Winning Chances: 21.37% (G:0.00% B:0.00%)
Double/Take
Player Winning Chances: 78.71% (G:0.01% B:0.00%)
Opponent Winning Chances: 21.29% (G:0.00% B:0.00%)

Cubeless Equities: No Double=+0.573, Double=+1.149

Cubeful Equities:
No double: +0.890 (-0.110)
Double/Take: +1.016 (+0.016)
Double/Pass: +1.000

Best Cube action: Double / Pass

Rollout:
842 Games rolled with Variance Reduction.
Moves and cube decisions: XG Roller+
Search interval: Gigantic
Confidence No Double: ± 0.006 (+0.884..+0.896)
Confidence Double: ± 0.008 (+1.007..+1.024)

Double Decision confidence: 100.0%
Take Decision confidence: 100.0%

Duration: 9 hours 19 minutes

eXtreme Gammon Version: 2.19.211.pre-release


XGID=-B--A-DACA--dC---d-dc-----:0:0:1:00:0:0:3:0:1X:Player 2 O:Player 1
0

Score is X:0 O:0. Unlimited Game, Jacoby Beaver

+13-14-15-16-17-18------19-20-21-22-23-24-+
| X O | | O O |
| X O | | O O |
| X O | | O O |
| O | | O |
| | | |
| |BAR| |
| | | |
| O | | X |
| O X | | X |
| O 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: 109 O: 123 X-O: 0-0

Cube: 1
X on roll, cube action

Analyzed in Rollout
No double
Player Winning Chances: 78.63% (G:0.01% B:0.00%)
Opponent Winning Chances: 21.37% (G:0.00% B:0.00%)
Double/Take
Player Winning Chances: 78.71% (G:0.01% B:0.00%)
Opponent Winning Chances: 21.29% (G:0.00% B:0.00%)

Cubeful Equities:
No double: +0.890 (-0.110)
Double/Take: +1.016 (+0.016)
Double/Pass: +1.000

Best Cube action: Double / Pass

Rollout:
842 Games rolled with Variance Reduction.
Moves and cube decisions: XG Roller+
Search interval: Gigantic
Confidence No Double: ± 0.006 (+0.884..+0.896)
Confidence Double: ± 0.008 (+1.007..+1.024)

eXtreme Gammon Version: 2.19.211.pre-release

---
Tim Chow