2A 2A play has been discussed ad nauseam and it would be tedious to
rehash the details.
Since, barring any checker blunders, doubling at the first opportunity is
a version of optimal play, I was slightly surprised at XG's hold here.
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?
Any comments? I suppose occasionally XG will do something that a human
will see as clearly non-optimal (or at least
questionable). One of XG's evaluations is clearly slightly wrong but that
might just be the price of the coding design.

It reminds me of a position where XG had all its checkers and I had a single
checker. My checker was on my deuce point, XG held my ace point and XG
was on roll. If XG can't hit me and can't run off the backgammon then any player who isn't a rank beginner knows to hold the ace point hoping for the one percent parlay where I roll 11 and the opponent hits. 1% really isn't so small. But XG just ran off my acepoint with one checker and conceded the backgammon.
This evaluation seems kind of like that.

Having said all this, I now clearly remember that at 2A, 2A with my 52,
holding is actually fine because XG's best sequence is 55, dance, which
is a clear take.
However, the determination that doubling is wrong seems suspect?

Paul

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

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

Analyzed in XG Roller+
Player Winning Chances: 49.72% (G:14.79% B:1.11%)
Opponent Winning Chances: 50.28% (G:15.26% B:1.91%)

Cubeless Equities: No Double=-0.014, Double=-0.022

Cubeful Equities:
No double: -0.015
Double/Take: -0.022 (-0.007)
Double/Pass: +1.000 (+1.015)

Best Cube action: No double / Take
Percentage of wrong pass needed to make the double decision right: 0.7%

eXtreme Gammon Version: 2.10, MET: Kazaross XG2

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

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.

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

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?

Paul

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

On Friday, December 29, 2023 at 1:18:14 PM UTC-5, peps...@gmail.com wrote:
> 2A 2A play has been discussed ad nauseam and it would be tedious to
> rehash the details.
> Since, barring any checker blunders, doubling at the first opportunity is
> a version of optimal play, I was slightly surprised at XG's hold here.
> 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?
> Any comments? I suppose occasionally XG will do something that a human
> will see as clearly non-optimal (or at least
> questionable). One of XG's evaluations is clearly slightly wrong but that
> might just be the price of the coding design.
>
> It reminds me of a position where XG had all its checkers and I had a single
> checker. My checker was on my deuce point, XG held my ace point and XG
> was on roll. If XG can't hit me and can't run off the backgammon then any player who isn't a rank beginner knows to hold the ace point hoping for the one percent parlay where I roll 11 and the opponent hits. 1% really isn't so small. But XG just ran off my acepoint with one checker and conceded the backgammon.
> This evaluation seems kind of like that.
>
> Having said all this, I now clearly remember that at 2A, 2A with my 52,
> holding is actually fine because XG's best sequence is 55, dance, which
> is a clear take.
> However, the determination that doubling is wrong seems suspect?
>
> Paul
>
> XGID=-b----E-D---eD---c-e--A-A-:0:0:-1:00:9:9:0:11:10
>
> X:XG Roller+ O:Daniel
> Score is X:9 O:9 11 pt.(s) match.
> +13-14-15-16-17-18------19-20-21-22-23-24-+
> | X O | | O X |
> | X O | | O X |
> | X O | | O |
> | X O | | O |
> | X | | O |
> | |BAR| |
> | | | X |
> | O | | X |
> | O X | | X |
> | O X | | X |
> | O X | | X O O |
> +12-11-10--9--8--7-------6--5--4--3--2--1-+
> Pip count X: 167 O: 160 X-O: 9-9/11
> Cube: 1
> X on roll, cube action
>
> Analyzed in XG Roller+
> Player Winning Chances: 49.72% (G:14.79% B:1.11%)
> Opponent Winning Chances: 50.28% (G:15.26% B:1.91%)
>
> Cubeless Equities: No Double=-0.014, Double=-0.022
>
> Cubeful Equities:
> No double: -0.015
> Double/Take: -0.022 (-0.007)
> Double/Pass: +1.000 (+1.015)
>
> Best Cube action: No double / Take
> Percentage of wrong pass needed to make the double decision right: 0.7%
>
> eXtreme Gammon Version: 2.10, MET: Kazaross XG2

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

Stick

On Monday, January 1, 2024 at 7:49:02 PM UTC, Stick Rice wrote:
> On Friday, December 29, 2023 at 1:18:14 PM UTC-5, peps...@gmail.com wrote:
> > 2A 2A play has been discussed ad nauseam and it would be tedious to
> > rehash the details.
> > Since, barring any checker blunders, doubling at the first opportunity is
> > a version of optimal play, I was slightly surprised at XG's hold here.
> > 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?
> > Any comments? I suppose occasionally XG will do something that a human
> > will see as clearly non-optimal (or at least
> > questionable). One of XG's evaluations is clearly slightly wrong but that
> > might just be the price of the coding design.
> >
> > It reminds me of a position where XG had all its checkers and I had a single
> > checker. My checker was on my deuce point, XG held my ace point and XG
> > was on roll. If XG can't hit me and can't run off the backgammon then any player who isn't a rank beginner knows to hold the ace point hoping for the one percent parlay where I roll 11 and the opponent hits. 1% really isn't so small. But XG just ran off my acepoint with one checker and conceded the backgammon.
> > This evaluation seems kind of like that.
> >
> > Having said all this, I now clearly remember that at 2A, 2A with my 52,
> > holding is actually fine because XG's best sequence is 55, dance, which
> > is a clear take.
> > However, the determination that doubling is wrong seems suspect?
> >
> > Paul
> >
> > XGID=-b----E-D---eD---c-e--A-A-:0:0:-1:00:9:9:0:11:10
> >
> > X:XG Roller+ O:Daniel
> > Score is X:9 O:9 11 pt.(s) match.
> > +13-14-15-16-17-18------19-20-21-22-23-24-+
> > | X O | | O X |
> > | X O | | O X |
> > | X O | | O |
> > | X O | | O |
> > | X | | O |
> > | |BAR| |
> > | | | X |
> > | O | | X |
> > | O X | | X |
> > | O X | | X |
> > | O X | | X O O |
> > +12-11-10--9--8--7-------6--5--4--3--2--1-+
> > Pip count X: 167 O: 160 X-O: 9-9/11
> > Cube: 1
> > X on roll, cube action
> >
> > Analyzed in XG Roller+
> > Player Winning Chances: 49.72% (G:14.79% B:1.11%)
> > Opponent Winning Chances: 50.28% (G:15.26% B:1.91%)
> >
> > Cubeless Equities: No Double=-0.014, Double=-0.022
> >
> > Cubeful Equities:
> > No double: -0.015
> > Double/Take: -0.022 (-0.007)
> > Double/Pass: +1.000 (+1.015)
> >
> > Best Cube action: No double / Take
> > Percentage of wrong pass needed to make the double decision right: 0.7%
> >
> > eXtreme Gammon Version: 2.10, MET: Kazaross XG2
> The bot shouldn't double at 2a 2a unless it sees at least one market losing sequence. Are there any MLS here?

No, there aren't. I learned that quite early on FIBS in the nineties.
I criticised my opponent for not doubling immediately and he replied that doubling is unnecessary because 55/dance
is still a take because gammons aren't in play.

Paul

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

On Monday, January 1, 2024 at 5:45:40 PM UTC-5, Timothy Chow wrote:
> 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

They don't, but they do.

Stick