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Two positions and an Intro

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Klaus G Wagner

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Jan 3, 1997, 3:00:00 AM1/3/97
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From two recent FIBS matches:

X to play 51.

+-1--2--3--4--5--6--------7--8--9-10-11-12-+ O: OOOOO - score: 2
| X O | | X O O X |
| X O | | O X |
| O | | O X |
| O | | O X |
| O | | |
| |BAR| |v 7-point match
| | | |
| X | | O |
| X | | X O |
| X | | X O |
| X O X | | X O |
+24-23-22-21-20-19-------18-17-16-15-14-13-+ X: kgw - score: 2
BAR: O-0 X-0 OFF: O-0 X-0 Cube: 2 (owned by kgw)


I played 1-2-7, thinking of nothing else ...
gepard (my 9 year old son Gerhard) would prefer 17-22*-23.
Which one is best? Or is it something else? ( surprise! :)

BTW, ye Stronger Ones out there on FIBS:
If you'd like to play a bright child, please *play gepard* .
After starting to play BG about half a year ago, he began on FIBS
by reaching about 1650 and is now working his way up from 1550
after losing a couple of really nasty matches (referring to the
dice, of course, not to the opponents :) Anyway, he produces good,
thrilling games, and locally around here the opponents are scarce,
and I almost cannot teach him anything more on BG ... so if *you*
feel like it, come on!!

The second position:

X on roll. Cube Action?

+13-14-15-16-17-18-------19-20-21-22-23-24-+ X: XXX - score: 2
| O X X X | X | X O |
| O X X | | X |
| O X | | X |
| | | X |
| | | X |
v| |BAR| | 5-point match
| | | |
| | | |
| | | O |
| X O | | O O O |
| X O O | | O O X O O |
+12-11-10--9--8--7--------6--5--4--3--2--1-+ O: kgw - score: 2

BAR: O-0 X-1 OFF: O-0 X-0 Cube: 1 turn: kgw

I doubled (after a dance by X), XXX dropped (and went on to win
the match by a narrow margin).

Afterwards, I wondered about whether playing on for the gammon would
have been better. There are 15/36 chances to make the 4 point, and most
other rolls are constructive too (except maybe 65). On the other hand,
X surely is not finished yet.

What do you think?

Greetings and much luck to you all (as long as you don't play _me_ ;-)

kgw

--
Klaus G. Wagner k...@watari.franken.de
D-97218 Gerbrunn
PGP (1024/D7A16B1D) = 42 5B CD ED EC E7 8F 50 C0 B0 14 1E 3B 9F DC 08
--
Klaus G. Wagner k...@watari.franken.de
D-97218 Gerbrunn
PGP (1024/D7A16B1D) = 42 5B CD ED EC E7 8F 50 C0 B0 14 1E 3B 9F DC 08

Klaus G Wagner

unread,
Jan 4, 1997, 3:00:00 AM1/4/97
to

k...@watari.franken.de (Klaus G Wagner) wrote:

> X on roll. Cube Action?

^^^^^^^^^
Oops ... O on roll, of course! Sorry for the mistake.

> +13-14-15-16-17-18-------19-20-21-22-23-24-+ X: XXX - score: 2
> | O X X X | X | X O |
> | O X X | | X |
> | O X | | X |
> | | | X |
> | | | X |
> v| |BAR| | 5-point match
> | | | |
> | | | |
> | | | O |
> | X O | | O O O |
> | X O O | | O O X O O |
> +12-11-10--9--8--7--------6--5--4--3--2--1-+ O: kgw - score: 2

> BAR: O-0 X-1 OFF: O-0 X-0 Cube: 1 turn: kgw

--

Chuck Bower

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Jan 5, 1997, 3:00:00 AM1/5/97
to

In article <E3GGJ...@watari.franken.de>,

Klaus G Wagner <k...@watari.franken.de> wrote:
> From two recent FIBS matches:
>
> X to play 51.
>
> +-1--2--3--4--5--6--------7--8--9-10-11-12-+ O: OOOOO - score: 2
> | X O | | X O O X |
> | X O | | O X |
> | O | | O X |
> | O | | O X |
> | O | | |
> | |BAR| |v 7-point match
> | | | |
> | X | | O |
> | X | | X O |
> | X | | X O |
> | X O X | | X O |
> +24-23-22-21-20-19-------18-17-16-15-14-13-+ X: kgw - score: 2
> BAR: O-0 X-0 OFF: O-0 X-0 Cube: 2 (owned by kgw)
>
>
> I played 1-2-7, thinking of nothing else ...
> gepard (my 9 year old son Gerhard) would prefer 17-22*-23.
> Which one is best? Or is it something else? ( surprise! :)
>

Jellyfish level-7 evaluation agrees with Gebhard: 17/22*/23 is better
than 1/7 by 0.10 units (cubeless money equity) which is quite a bit, BTW.
Good news is that you and the lad found the two best plays. (Note that
the match score doesn't alter the "correct play" in this case.)

(snip)
>
> The second position:


>
> X on roll. Cube Action?
>

> +13-14-15-16-17-18-------19-20-21-22-23-24-+ X: XXX - score: 2
> | O X X X | X | X O |
> | O X X | | X |
> | O X | | X |
> | | | X |
> | | | X |
> v| |BAR| | 5-point match
> | | | |
> | | | |
> | | | O |
> | X O | | O O O |
> | X O O | | O O X O O |
> +12-11-10--9--8--7--------6--5--4--3--2--1-+ O: kgw - score: 2
>
> BAR: O-0 X-1 OFF: O-0 X-0 Cube: 1 turn: kgw
>

> I doubled (after a dance by X), XXX dropped (and went on to win
> the match by a narrow margin).
>
> Afterwards, I wondered about whether playing on for the gammon would
> have been better. There are 15/36 chances to make the 4 point, and most
> other rolls are constructive too (except maybe 65). On the other hand,
> X surely is not finished yet.
>
> What do you think?
>

You really want to know? OK, but you asked for it.... Actually, knowing
when to cash and when to play on for gammon is one of the least discussed
(and therefore, quite possibly one of the least understood) areas of the
game. Fortunately for us (well, you and me, anyway), Rick Janowski wrote
an excellent series of articles a couple years ago in "Hoosier BG
Newsletter". FOR MONEY PLAY, he gives the following formula for the
"TOO GOOD (to redouble) POINT", assuming "typical" cube ownership equity:

L + 1
If game winning chances greater than: -------------
W + L + 0.333

then play on for the gammon. L and W are (respectively) the average losing
and winning expectations (cubeless) for the player making the decision (O in
this case). These can easily be calculated from JF rollout (or evaluation)
results as illustrated below. JF rollout (108 trials on level-6 cubeless)
gave the following results:

simple g+bg bg
O wins 75.9 50.6 1.4
X wins 24.1 5.0 0.4

(cubeless equity = 0.983, std. dev. = 0.024, equiv. to 3107 games).

From O's point of view, W = (75.9 + 50.6 + 1.4)/75.9 = 1.685 and
L = (24.1 + 5.0 + 0.4)/24.1 = 1.224

So, the cutoff point for playing on for the gammon is:

(1.224 + 1) / (1.685 + 1.224 + 0.333) = 68.6%

And since JF sez O wins 75.9% (which is more than 68.6%), O should play
on for the gammon at money play. As far as this particular match score,
I did the math (but save the reader the multiple lines here) which shows
the following (assuming the gammon fractions indicated by the rollout):

X's drop point for money: 36.5%
X's drop point at this match score: 40%

As you can see, X should be MORE LIKELY to drop this position at this match
score (assuming the large gammon fraction indicated by the rollout) so
playing on for the gammon is even more likely to work than at money play.
(As always, there is some argument for doubling IF you think your opponent
might take. In this case taking looks rather foolish.)

One final note: Rick's formula appears to diverge from "reality"
when gammons chances go to zero, since then you would expect the formula
to give 1.00, which it doesn't. Maybe he can comment on this.


Chuck
bo...@bigbang.astro.indiana.edu
c_ray on FIBS


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