Re: [Bug-gnubg] Bearoff dB position, few questions

[Christian Anthon]

The two-sided cubeful bearoff db is exact and used in preference of
evalutation, but only for moneygame.

Christian.

On Fri, Jun 19, 2009 at 3:56 PM, Massimiliano
Maini<address@hidden> wrote:
>
> Hi all,
>
> 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)
>
> Hint shows this:
>
> Cube analysis
> 2-ply cubeless equity  +0.4971
>   0.7485 0.0000 0.0000 - 0.2515 0.0000 0.0000
> Cubeful equities:
> 1. Double, take         +0.9158
> 2. Double, pass         +1.0000  ( +0.0842)
> 3. No double            +0.7661  ( -0.1496)
> Proper cube action: Redouble, take
>
> From eval (ctrl+E) I see (uninteresting parts removed):
>
> Position ID:        6AUAADoDAAAAAA
> Match ID:        UQlgAAAAAAAA
>
> Evaluator:         Bearoff2
>
>              Player       Opponent
> Position          880           912
>
>         Win     W(g)    W(bg)   L(g)    L(bg)   Equity    Cubeful
> static: 0.7485  0.0000  0.0000  0.0000  0.0000   +0.4971   +0.7661
>  1 ply: 0.7485  0.0000  0.0000  0.0000  0.0000   +0.4971   +0.7661
>  2 ply: 0.7485  0.0000  0.0000  0.0000  0.0000   +0.4971   +0.7661
>
> 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)
>
> Cube analysis
> 2-ply cubeless equity  +0.4797 (Money:  +0.4797)
>   0.7399 0.0000 0.0000 - 0.2601 0.0000 0.0000
> Cubeful equities:
> 1. Double, take         +0.9565
> 2. Double, pass         +1.0000  ( +0.0435)
> 3. No double            +0.7841  ( -0.1724)
> Proper cube action: Redouble, take
>
>         Win     W(g)    W(bg)   L(g)    L(bg)   Equity    Cubeful
> static: 0.7485  0.0000  0.0000  0.0000  0.0000   +0.4971   +0.8543
>  1 ply: 0.7399  0.0000  0.0000  0.0000  0.0000   +0.4797   +0.8308
>  2 ply: 0.7399  0.0000  0.0000  0.0000  0.0000   +0.4797   +0.7841
>
> 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
>
>
> Dump of position ID: 6AUAADoDAAAAAA
>
>              Player       Opponent
> Position          880           912
>
> Cubeless equity               : +0.4971
> Owned cube                    : +0.7661
> Centered cube                 : +0.7451
> Opponent owns cube            : +0.4579
>
> But I had no success in using the -n option (enter directly the
> position indexes, 880 and 921): how is this supposed to work ?
>
> MaX.
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