on a forum I've found this: same position
(in 2-sided bearoff dB)
in money play and match play (3aw-3aw)
shows different cubeless
equities. I tried to explain it but
I run into some confusion.
That's money play:
GNU Backgammon Position
ID: 6AUAADoDAAAAAA
Match ID : UQkAAAAAAAAA
+24-23-22-21-20-19------18-17-16-15-14-13-+
O: gnubg
OO |
O O O | |
| 0 points
OO |
O | |
|
OO |
O | |
|
OO |
O | |
|
O |
| |
|
|
|BAR|
|v
X |
| |
|
XX |
| |
|
XX |
X | |
|
XX |
X X | |
| On roll
XX | X X
X | |
| 0 points
+-1--2--3--4--5--6-------7--8--9-10-11-12-+
X: MaX (Cube: 2)
Static, 1ply and 2ply figures are identical,
which makes me think they all
come from the 2s bearoff dB (eval output
is a bit confusing here).
That's the same for match:
GNU Backgammon Position
ID: 6AUAADoDAAAAAA
Match ID : UQlgAAAAAAAA
+24-23-22-21-20-19------18-17-16-15-14-13-+
O: gnubg
OO |
O O O | |
| 0 points
OO |
O | |
|
OO |
O | |
|
OO |
O | |
|
O |
| |
|
|
|BAR|
|v 3 point match
X |
| |
|
XX |
| |
|
XX |
X | |
|
XX |
X X | |
| On roll
XX | X X
X | |
| 0 points
+-1--2--3--4--5--6-------7--8--9-10-11-12-+
X: MaX (Cube: 2)
The original question was: why the
2-ply cubeless GWC are different
between money and match ?
First answer was: it's using bearoff
dB from money and not for match.
Objection was that gnubg could/should
use the dB even for match, at
least for the cubeless GWC figures.
Here I tried to explain that cubefull
figures from the dB can only be
used in money play, but what about
cubeless ? Are cubeless figures from
the dB used as a base for cubefull
eval in match play ?
Looking at the figures I would say
yes: the static cubeless GWC for match
are exactly the ones you have in money.
But they diverge at 1 and 2 ply.
Am I right if I say that doing 2ply
eval in match, gnubg needs to compute
a lot of 0ply cubeless evals and it
takes them from the dB. The figures
are converted into 0ply cubeful (Janowski
formula) and then "backpropagated"
to get 2ply cubeful. 2ply cubeless
is computed by inversing the Janowski
formula on 2ply cubeful figures.
If all the above is true, I do see
the objection coming: it's true that what
matter are cubeful figures (and these
cannot be taken from the dB in match),
but why gnubg isn't showing the "right"
cubeless GWC (the ones from the dB)
in match ?
Side question: I tried to use bearoffdump.
I manage to get the info putting
in the position ID:
D:\Documents\gnubg>bearoffdump.exe
-p 6AUAADoDAAAAAA gnubg_ts0.bd
Bearoff database: gnubg_ts0.bd
Position ID : 6AUAADoDAAAAAA
Information about database:
* On disk 2-sided bearoff database
evaluator
- generated by GNU Backgammon
- up to 6 chequers on
6 points (924 positions) per player
- database includes both
cubeful and cubeless equities
- number of reads: 0