I correctly, and somewhat confidently took below.
Why? Because I have a clear memory of listening to a youtube
lecture by Mochy where he gave a very similar position and explained
that although we know the slogan "three roll positions are passes", the
fact that the cuber has one number (21) that loses immediately is enough
to swing the position to a take.
I think that Mochy's position differs from mine only in that all O's
six checkers are piled on the ace.
So my position is worse than in Mochy's example but only very slightly
worse and therefore still a take.

Moral of the story: Do listen to Mochy.

XGID=-DB-------------------a-e-:2:-1:-1:00:0:4:3:0:10
X:eXtremeGammon O:Daniel

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

Analyzed in 4-ply
Player Winning Chances: 76.13% (G:0.00% B:0.00%)
Opponent Winning Chances: 23.87% (G:0.00% B:0.00%)

Cubeless Equities: No Double=+0.523, Double=+1.045

Cubeful Equities:
No redouble: +0.702 (-0.247)
Redouble/Take: +0.949
Redouble/Pass: +1.000 (+0.051)

Best Cube action: Redouble / Take

eXtreme Gammon Version: 2.10

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On 12/4/2021 8:26 AM, peps...@gmail.com wrote:

I correctly, and somewhat confidently took below.
Why? Because I have a clear memory of listening to a youtube
lecture by Mochy where he gave a very similar position and explained
that although we know the slogan "three roll positions are passes", the
fact that the cuber has one number (21) that loses immediately is enough
to swing the position to a take.

Very nice!

Do you have specific Mochy videos that you recommend? Here's one of
my favorites:

https://www.youtube.com/watch?v=omWy4xng88I

---
Tim Chow

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On 2021-12-04, peps...@gmail.com <pepstein5@gmail.com> wrote:

XGID=-DB-------------------a-e-:2:-1:-1:00:0:4:3:0:10
X:eXtremeGammon O:Daniel

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

Analyzed in 4-ply
Player Winning Chances: 76.13% (G:0.00% B:0.00%)
Opponent Winning Chances: 23.87% (G:0.00% B:0.00%)

Cubeless Equities: No Double=+0.523, Double=+1.045

Cubeful Equities:
No redouble: +0.702 (-0.247)
Redouble/Take: +0.949
Redouble/Pass: +1.000 (+0.051)

Best Cube action: Redouble / Take

eXtreme Gammon Version: 2.10

Strange anaysis result. In such a short race the equities can be
calculated exactly (and are probably in a bearoff database). No redouble
shoud be 0.700, Redouble/Take 0.980. How can XG get these wrong when all
its other numbers are accurate ?

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On 12/15/2021 5:59 PM, Philippe Michel wrote:

Strange anaysis result. In such a short race the equities can be
calculated exactly (and are probably in a bearoff database). No redouble shoud be 0.700, Redouble/Take 0.980. How can XG get these wrong when all
its other numbers are accurate ?

It gets it right with 5-ply or higher (which corresponds to GNU 4-ply
or higher). So my guess is that a 4-ply evaluation is effectively
a "truncated rollout" with the checker play being governed by the
neural net directly, and the truncated evaluation also being calculated
by consulting the net rather than the database?

---
Tim Chow

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On Thursday, December 16, 2021 at 1:48:58 AM UTC, Tim Chow wrote:

On 12/15/2021 5:59 PM, Philippe Michel wrote:

Strange anaysis result. In such a short race the equities can be
calculated exactly (and are probably in a bearoff database). No redouble shoud be 0.700, Redouble/Take 0.980. How can XG get these wrong when all its other numbers are accurate ?

It gets it right with 5-ply or higher (which corresponds to GNU 4-ply
or higher). So my guess is that a 4-ply evaluation is effectively
a "truncated rollout" with the checker play being governed by the
neural net directly, and the truncated evaluation also being calculated
by consulting the net rather than the database?
as

It's interesting that XG made an error here. I was actually surprised to see a take
as big as 0.95 -- 0.98 is more in line with what I would have expected.

Paul

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On 2021-12-16, Timothy Chow <tchow12000@yahoo.com> wrote:

On 12/15/2021 5:59 PM, Philippe Michel wrote:

Strange anaysis result. In such a short race the equities can be
calculated exactly (and are probably in a bearoff database). No redouble
shoud be 0.700, Redouble/Take 0.980. How can XG get these wrong when all
its other numbers are accurate ?

It gets it right with 5-ply or higher (which corresponds to GNU 4-ply
or higher). So my guess is that a 4-ply evaluation is effectively
a "truncated rollout" with the checker play being governed by the
neural net directly, and the truncated evaluation also being calculated
by consulting the net rather than the database?

It's certainly a possibility, but then in what circumstances is the
bearoff database used ?

It makes sense that the evaluation can (and should, really) stop early
in regular play or rollouts: for instance on an opening 3-1, 1-ply
probably sees 8/5 6/5 best by a margin wide enough that there is no need
to go to higher plies.

On the other hand when analyzing we may be interested by the equities of
the better plays, not just which one comes on top. Then evaluating the
first few plays at the required ply is fine.

But the two-sided bearoff database is perfect (for money play) and
querying it is fast. It seems wrong not to use it rather than any ply or
roller level when the position allows it,

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On 12/17/2021 5:01 PM, Philippe Michel wrote:

It's certainly a possibility, but then in what circumstances is the
bearoff database used ?

I just looked in the XG help. It's not clear on this point.
Here is the most relevant line I found:

---------
There are 2 reasons for using larger databases:
* The EPC can be calculated (see Race formulae for more
information about EPC)
* The program is slightly more accurate in the race.
---------

So the bearoff database is used to calculate EPC. But it's not
clear in what other circumstances the bearoff database is actually
used. You might think that when you play against the computer, it
uses the bearoff database when bearing off. Or you might think that
if you do a rollout and select the "Truncate in Bearoff" option, then
when it truncates, it will consult the bearoff database. But I was
not able to find any explicit statement to this effect in the help.

---
Tim Chow

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