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Re: [Bug-gnubg] Suspect bearoff results
From: |
Joern Thyssen |
Subject: |
Re: [Bug-gnubg] Suspect bearoff results |
Date: |
Sun, 15 Dec 2002 18:03:04 +0000 |
User-agent: |
Mutt/1.4i |
On Fri, Dec 13, 2002 at 03:01:48PM -0000, Ian Shaw wrote
> GNU Backgammon Position ID: qMduAwDYvmgDAA
> Match ID : cAkrAAAAAAAA
> +24-23-22-21-20-19------18-17-16-15-14-13-+ O: GnuBg
> | O O O | | O O O O | 0 points
> | O | | O O O O |
> | O | | O |
> | O | | |
> | | | |
> | |BAR| |v 1 point match (Cube: 1)
> | X | | |
> | X | | |
> | X | | |
> | X X X | | X X | Rolled 62
> | X X X | | X X X X | 0 points
> +-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: Ian
>
> Does it really make no difference what I play here? I guess it's
> possible since the position is so flexible, but I'd like reassurance
> that the database is working correctly.
>
> Why is there a 2-ply or 0-ply evaluation when it is all being looked
> up in a database?
It can't calculate cubeful equities using the database (except money
game and a position in the two-sided database).
I agree that for some match scores (like this one), there is no need to
recurse multiple ply as the cube is dead.
> This also takes a lot longer to come up with a hint than if I use the
> race net (temporarily renaming gnubg_os.bd and restart).
Reading from the two-sided bearoff database is currently quite
inefficient. It's on my TODO list to improve this. gnubg caches
evaluations of positions, but for the one-sided bearoff database we need
to cache one-sided positions as well.
> Is this to be expected? Are the results needlessly looked up multiple
> times for the different plies?
Some bearoff distributions may be needlessly looked up, but as I
mentioned above, we cannot avoid the recursing (except for special match
scores -- which is not implemented).
The race net returns approximately the results as the one-sided bearoff.
You can setup the board after 12/6 7/5 and 11/5 7/5 and using the
"Evaluate" command you get some extra output from the bearoff database.
Here is the bearoff distribution for the to moves:
2 0.000 0.000
3 0.000 0.000
4 0.000 0.000
5 0.000 0.000
6 0.002 0.003
7 0.031 0.031
8 0.229 0.229
9 1.044 1.044
10 3.459 3.458
11 8.357 8.354
12 15.311 15.314
13 21.118 21.117
14 21.755 21.756
15 16.394 16.394
16 8.551 8.551
17 2.962 2.962
18 0.674 0.674
19 0.102 0.102
20 0.011 0.011
21 0.000 0.000
22 0.000 0.000
23 0.000 0.000
24 0.000 0.000
These look very similar and as the opponents distribution is the same it
seems fair that the two distributions result in the same winning
probability.
Jørn