Jim Segrave <[EMAIL PROTECTED]> wrote on 13/11/2007 22:51:14:
> The game is played out with the cube on 2, sometimes that leads to a
> redouble/take with the cube on 4. Gnubg plays both sides optimally
> (from gnubg's point of view) and terminates a rollout of a game when:
>
> one side wins outright
>
> or
>
> one side doubles and the response is drop
>
> or
>
> the preset maximum number of moves has been rolled out, in which case
> the evaluation of win/lose gammon/backgammon is used to assign a
> result other than plus or minus 1/2/4/8 or whatever cube value might
> apply
>
>
> > 2- At the end of the trials, the computed "cubeless" figures will
> > lead to a "cubeless" equity that will be translated into a cubefull
> > equity via the janowski formula, right? In Mochy's example, the
W/G/BG%
> > are the "cubeless" results of the rollout, the CL is the "cubeless"
> > equity and CF is comuted via Janowski formula?
>
> Yes, but during the rollout the cube value can change, so the
> approximated equity is multiplied by the current cube value (with
> allowances for a cube which is greater than the value needed to win a
> match for non-money games)
Hi Jim,
I think it just doesn't work like this. I give you an example:
let's say I'm playing a money session and I do a full cubefull rollout
(no truncation whatsoever). Let's say that in 90% of the trials, player
1 wins 1 point while in 10% of the trials, player 2 wins 1 points.
In terms of w/g/bg - l/g/bg this makes 0.9/0/0.0 - 0.1/0.0/0.0.
But what happens if, in the same situation, all the 10% of player 2 simple
wins happens with the cube at 16 because of a series of double/take
happened in these trials ?
I suspect it will still produce 0.9/0/0.0 - 0.1/0.0/0.0, but a totally
differest (estimated) cubeful equity (much more favorable to player 2).
I've found this post on the list archive (look at the entire thread):
http://lists.gnu.org/archive/html/bug-gnubg/2003-07/msg00543.html
It answers most of my questions:
- a cubefull rollout directly estimates the cubeful equity, the janowski
formula is not used.
- w/g/bg - l/g/bg are computed using actual results (number of simlpe,
gammon and backgammon wins and losses), independently from the cube
value (at the monent of the win/loss). When the rollout is truncated
(db position or double/pass or max number of plies), the cubeless eval
result (w/g/bg - l/g/bg) is used as result for this trial.
- the only meaningful figure to look at after a cubeful rollout (and
probably also after a cubeful evaluation) is the cubeful equity.
w/g/bg - l/g/bg may be more or less meaningless (and the cubeless
equity deduced from them too).
I don't know if I agree with Joern when he says that w/g/bg - l/g/bg
could even be removed from the output of any cubeful rollout/eval.
For sure we should make it very clear that w/g/bg - l/g/bg are
not really reliable in cubeful rollouts and in cubeful evals, when
the position may lead to cube action, since they do not tale into
account the cbe value.
MaX.
P.S.
According to Christian's and Joern comments, in case of a double/drop,
the eval w/g/bg - l/g/bg (cubeless) will be used as result of the trial
in order to compute the overall (cubeless, in a certain sense) figures
for w/g/bg - l/g/bg. But the cubeful equity of this trial (used to
compute the overall cubeful equity) would be +1, right ?
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