"Christian Anthon" <address@hidden>
wrote on 14/04/2008 12:56:38:
> This the odd/even ply problem at its worst. First of all the
cube
> action is strange because gnubg grossly mis-evaluates the position
for
> one or both sides. Look at Max' examples and I'm sure you can come
up
> with a reasonable explanation.
>
> So, is it a bug in the code or in the net(s)? This is actually quite
> easy to test in this particular case!
>
> First of all set up the position and press ctrl-e (or select eval
> under the analyse menu) and you get:
> -----
> Position ID: BwAAmG1bCkEAAA
> Match ID: UQngARAAIAAA
>
> Evaluator: CRASHED
>
> Win W(g) W(bg)
L(g) L(bg) Equity Cubeful
> static: 0.653 0.000 0.000 0.002 0.000
+0.304 +0.495
> -----
> assuming that you evaluating at 0ply.
>
> Next: I'm sure that we can all agree that it doesn't matter much what
> X rolls next. So let's just give him a 62 played 19/11 (wrongly I'm
> sure). Make sure that O is now on roll and eval the position again:
>
> ----
> Position ID: tm2pCAAHAAAYAA
> Match ID: EQHgARAAIAAA
>
> Evaluator: CRASHED
>
>
> Win W(g) W(bg)
L(g) L(bg) Equity Cubeful
> static: 0.185 0.003 0.001 0.000 0.000
-0.626 -0.866
> -----
>
> As you can see X's 0ply cubeless winning chances are 0.653, while
the
> 1ply cubeless winning chances are 1.0-0.185 = 0.815 (under the
> assumption that 19/11 is perfectly neutral).
>
> So its in the nets.
Not sure this answers the original questions raised
in Michael post:
Date: April 13, 2008
Move number 67: Monty on roll, cube decision? GNU Backgammon Position ID : BwAAmG1bCkEAAA
Match ID
: UQngARAAIAAA
+13-14-15-16-17-18------19-20-21-22-23-24-+ O: mpetch
| X | O | X
O | OO 1 point
| | O |
O | OO
| |
| O | OO
| |
| | OO
| |
| | OO
v| |BAR|
|
15 point match
| |
| |
| |
| |
| |
| |
| |
| X X X X X | On roll
| X X X | | X X
X X X | 4 points
+12-11-10--9--8--7-------6--5--4--3--2--1-+ X: Monty (Cube:
2)
Pip counts: O 53, X 99
Cubeful equities:
1. No double +1.015
2. Double, pass +1.000 ( -0.015)
3. Double, take +0.990 ( -0.025)
Proper cube action: Too good to redouble, take
Rollout details:
Player Monty owns 2-cube:
0.795 0.000 0.000 - 0.205 0.003 0.000 CL +0.587 CF +1.015
[0.001 0.000 0.000 - 0.001 0.000 0.000 CL 0.003 CF 0.005]
Player mpetch owns 4-cube:
0.800 0.000 0.000 - 0.200 0.004 0.001 CL +1.178 CF +0.990
[0.001 0.000 0.000 - 0.001 0.000 0.000 CL 0.006 CF 0.007]
- how can a position be too good for a player that
can not score a gammon ? Well, he could get backgammons, but it doesn't seem
to be the case above.
- how can a position be too good for player A and
be a take for player B ? I thought that, by definition, a position is too good
when my (normalized) equity is grater then +1.000. In this case, if doubled
my opponent should drop, losing only -1.000. Too good/take does not exist.
Maybe what's happening is this: rolling out the nodouble
part, X doubles later on and O takes. This can explain how X nodouble
equity is +1.015 > +1.000.
But the whole odd/even thing looks evil to me. For
example, take this position (same as previous but with closed board)
with black/X on roll:
GNU Backgammon Position ID: BwAA2LZtAUEAAA
Match ID : UQngARAAIAAA +13-14-15-16-17-18------19-20-21-22-23-24-+
O: gnubg | X
| O | X O
| OO 1 point |
| O |
O | OO |
| |
O | OO |
| |
| OO |
| |
| OO v|
|BAR|
| 15 point match |
| |
| |
| |
| |
| |
| |
| | X X X X X X
| On roll |
X | | X X X X X X |
4 points +12-11-10--9--8--7-------6--5--4--3--2--1-+
X: MaX (Cube: 2)
Position ID: BwAA2LZtAUEAAA Match ID: UQngARAAIAAA
GWC for X are 0.720 with X on roll and 0.866 with
white on roll ?!
> Christian, gladly demonstrating when the eval
function is a nice
> tool to have :)
Actually you can have exactly the same information
via the hint/analysis setting it to 0-ply. Only thing that's missing is
the used net (e.g. crushed) and the details at all the plies (e.g. setting
eval to 4 ply, with ctrl-E you get all the % at 0,1,2,3 and 4 ply,
while with hint you only get the 4ply figures).
MaX.
P.S. I start gnubg, open un the following sgf (position): http://www.gnubg.org/media/odd-pos-closed1.sgf
The player no the bar should be on roll. Enter edit mode and put the other playeron roll. Exit edit mode. Enter editmode again. Put the original player on roll (again). Exit edit mode. It crashes systematically.