On 12/29/2023 1:18 PM, peps...@gmail.com wrote:

I would not be surprised if the double was optional but I thought that the overriding goal of XG is to play as accurately as possible so, for the sake of coding simplicity, I was expecting a double here.

That is certainly not the overriding goal. If it were, then XG would use
some kind of massive bearoff database for bearing off, which it doesn't.
As for coding simplicity, adding a special feature to make it double at
the first opportunity at 2a2a is *less* simple than just letting it do
its normal thing, and there's no reason to expect that letting it do its
normal thing will cause it to double at the first opportunity at 2a2a.

---
Tim Chow

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On 2023-12-29, peps...@gmail.com <pepstein5@gmail.com> wrote:

I would not be surprised if the double was optional but I thought that the overriding goal of XG is to play as accurately as possible so, for the sake of coding simplicity, I was expecting a double here.
However, what I suspect is actually a bug is XG's determination that doubling is actually wrong. Surely doubling is fine even if holding is just as good?

Analyzed in XG Roller+

Maybe XG Roller+, a short truncated rollout with relatively low level evaluation of the leaf nodes, messes things up.

I would expect regular evaluations at 3-ply or more to find this is an
optional double / take.

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On 12/30/2023 2:10 AM, Philippe Michel wrote:

I would expect regular evaluations at 3-ply or more to find this is an optional double / take.

XGID=-b----E-D---eD---c-e--A-A-:0:0:-1:00:9:9:0:11:10

Score is X:9 O:9 11 pt.(s) match.
+12-11-10--9--8--7-------6--5--4--3--2--1-+
| X O | | O X X |
| X O | | O |
| X O | | O |
| X | | O |
| | | O |
| |BAR| |
| O | | X |
| O X | | X |
| O X | | X |
| O X | | X O |
| O X | | X O |
+13-14-15-16-17-18------19-20-21-22-23-24-+
Pip count X: 160 O: 167 X-O: 9-9/11
Cube: 1
O on roll, cube action

Analyzed in 3-ply
Player Winning Chances: 49.96% (G:14.31% B:1.17%)
Opponent Winning Chances: 50.04% (G:15.37% B:1.82%)

Cubeless Equities: No Double=-0.020, Double=-0.014

Cubeful Equities:
No double: -0.002
Double/Take: -0.014 (-0.012)
Double/Pass: +1.000 (+1.002)

Best Cube action: No double / Take
Percentage of wrong pass needed to make the double decision right: 1.2%

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

------------------------------------------------------------------------

XGID=-b----E-D---eD---c-e--A-A-:0:0:-1:00:9:9:0:11:10

Score is X:9 O:9 11 pt.(s) match.
+12-11-10--9--8--7-------6--5--4--3--2--1-+
| X O | | O X X |
| X O | | O |
| X O | | O |
| X | | O |
| | | O |
| |BAR| |
| O | | X |
| O X | | X |
| O X | | X |
| O X | | X O |
| O X | | X O |
+13-14-15-16-17-18------19-20-21-22-23-24-+
Pip count X: 160 O: 167 X-O: 9-9/11
Cube: 1
O on roll, cube action

Analyzed in 4-ply
Player Winning Chances: 49.96% (G:14.31% B:1.17%)
Opponent Winning Chances: 50.04% (G:15.37% B:1.82%)

Cubeless Equities: No Double=-0.020, Double=-0.004

Cubeful Equities:
No double: -0.002
Double/Take: -0.004 (-0.002)
Double/Pass: +1.000 (+1.002)

Best Cube action: No double / Take
Percentage of wrong pass needed to make the double decision right: 0.2%

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

---
Tim Chow

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On 12/30/2023 2:56 PM, peps...@gmail.com wrote:

On Saturday, December 30, 2023 at 4:57:30 AM UTC, Timothy Chow wrote:
...

As for coding simplicity, adding a special feature to make it double at
the first opportunity at 2a2a is *less* simple than just letting it do
its normal thing, and there's no reason to expect that letting it do its
normal thing will cause it to double at the first opportunity at 2a2a.

I assumed (with no justification whatsoever) that XG had some sort
of special feature whereby it normally doubled as soon as legal at 2A 2A.
If it did have some such feature (it probably doesn't) then code saying: [Always use that feature] would be simpler than code saying: [Use that feature unless...]

Assuming you're an expert on how XG works, where did you gain that
knowledge? Is it from public sources or personal correspondence
with Xavier?

I'm not an expert on how XG works, but this whole thread is presenting
evidence that XG has no such special feature. Since there is no evidence
that XG does have such a special feature, the preponderance of the
evidence suggests that no such special feature exists.

---
Tim Chow

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On 1/1/2024 2:49 PM, Stick Rice wrote:

The bot shouldn't double at 2a 2a unless it sees at least one market losing sequence. Are there any MLS here?

I'm not sure exactly what you're saying here, but just to be clear,
bots don't explicitly consider market-losing sequences when deciding
whether to double.

https://www.bgonline.org/forums/webbbs_config.pl?read=57030

---
Tim Chow

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