eXtreme Gammon book oddities

[Timothy Chow]

I have mentioned before that XG's book has some oddities,
such as rollouts with a single trial. Since mentioning that
here on r.g.b., I haven't run across that particular oddity,
but here are a couple of other oddities that I encountered
today.

In the first example, the "book" entry is for an obviously
ridiculous play. The obviously correct play is not in the book.

-------------------------------------------------------------------

XGID=-a--a-E-C---dE--ac-e----B-:0:0:1:42:3:5:0:7:10

X:Me O:eXtremeGammon
Score is X:3 O:5 7 pt.(s) match.
+13-14-15-16-17-18------19-20-21-22-23-24-+
| X O O | | O X |
| X O | | O X |
| X O | | O |
| X | | O |
| X | | O |
| |BAR| |
| | | X |
| O | | X |
| O X | | X |
| O X | | X |
| O X | | X O O |
+12-11-10--9--8--7-------6--5--4--3--2--1-+
Pip count X: 167 O: 160 X-O: 3-5/7
Cube: 1
X to play 42

1. 3-ply 8/4* 6/4 eq:+0.603
Player: 54.29% (G:17.34% B:0.83%)
Opponent: 45.71% (G:12.02% B:0.65%)

2. Book¹ 8/4* 4/2 eq:+0.012 (-0.591)
Player: 43.62% (G:11.06% B:0.41%)
Opponent: 56.38% (G:17.17% B:1.09%)

¹Generated by Dmitriy Obukhov on 6/7/2013 using eXtreme Gammon 2.00
Analyzed in XG Roller++

eXtreme Gammon Version: 2.19.207.pre-release, MET: Kazaross XG2

-------------------------------------------------------------------

In the second example, the "book" contains four possible plays, but
one of the most obvious candidates is not in the "book."

-------------------------------------------------------------------

XGID=-b----E-C---eE---c-e----B-:0:0:-1:54:4:5:0:7:10

X:Me O:eXtremeGammon
Score is X:4 O:5 7 pt.(s) match.
+12-11-10--9--8--7-------6--5--4--3--2--1-+
| X O | | O X |
| X O | | O X |
| X O | | O |
| X | | O |
| X | | O |
| |BAR| |
| O | | X |
| O | | X |
| O X | | X |
| O X | | X O |
| O X | | X O |
+13-14-15-16-17-18------19-20-21-22-23-24-+
Pip count X: 167 O: 167 X-O: 4-5/7
Cube: 1
O to play 54

1. 4-ply 24/15 eq:-0.146
Player: 50.43% (G:11.62% B:0.48%)
Opponent: 49.57% (G:13.05% B:0.48%)

2. Book¹ 24/20 13/8 eq:-0.189 (-0.043)
Player: 50.35% (G:15.61% B:2.23%)
Opponent: 49.65% (G:13.89% B:1.10%)
Confidence: ±0.003 (-0.192..-0.187) - [100.0%]

3. Book¹ 13/9 13/8 eq:-0.212 (-0.066)
Player: 49.66% (G:17.02% B:2.44%)
Opponent: 50.34% (G:14.05% B:1.61%)
Confidence: ±0.003 (-0.215..-0.209) - [0.0%]

4. Book² 13/4 eq:-0.282 (-0.137)
Player: 48.26% (G:15.68% B:1.98%)
Opponent: 51.74% (G:14.63% B:1.86%)
Confidence: ±0.005 (-0.287..-0.278) - [0.0%]

5. Book³ 13/8 6/2 eq:-0.364 (-0.218)
Player: 46.65% (G:13.40% B:0.71%)
Opponent: 53.35% (G:15.57% B:0.74%)

¹Generated by Steven Carey on 1/16/2013 using eXtreme Gammon 2.10
46656 Games rolled with Variance Reduction.
Dice Seed: 79034351
Moves: 3-ply, cube decisions: 4-ply

²Generated by Steven Carey on 8/1/2012 using eXtreme Gammon 2.10
15552 Games rolled with Variance Reduction.
Dice Seed: 162317
Moves: 3-ply, cube decisions: XG Roller

³Generated by GameSite 2000, Ltd on 5/21/2011 using eXtreme Gammon 2.00
Analyzed in XG Roller++

eXtreme Gammon Version: 2.19.207.pre-release, MET: Kazaross XG2

---
Tim Chow

[Philippe Michel]

On 2021-09-22, Timothy Chow <tchow...@yahoo.com> wrote:
> I have mentioned before that XG's book has some oddities,
> such as rollouts with a single trial. Since mentioning that
> here on r.g.b., I haven't run across that particular oddity,
> but here are a couple of other oddities that I encountered
> today.

As far as I understand, what is in XG's opening book is individual
positions not play decisions.

In you first example, it is unlikely the candidate positions for the
obvious 43Z-42 were added. On the other hand, maybe those for the less
clear 62R-43-61 were, and your 8/4*/2 comes from there while 8/4* 6/4
has to be evaluated.

For this example, it would be helpful to look at the 63 opening. Is
24/15 taken from the book there ? Then it should be available for 54.

A possible explanation would be that a move filter is somehow involved,
but there is no way 24/15 is worse than 13/8 6/2 or even 13/4 in a
shallower evaluation.

Anyway, the opening book and its format are available here:
http://www.extremegammon.com/GetOb.aspx

Someone motivated enough could look at what is really inside it and even
fix or extend it.