In defence of the 2-5 backgame
tc...@lsa.umich.edu
the claim that the 2-5 backgame is actually quite good.
Trice remarks that it's not too bad a rule of thumb to double a well-timed
backgame when you have three points left in front of the more advanced
anchor. Below are some examples from his book. These are all money-game
positions with X on roll, Snowie rollout results.
First I'll give examples of the 1-2, 1-3, and 2-3 backgames, just to give
us some feeling for what to expect. Then I'll give the 1-5 and 2-5 backgames.
The punchline is that for superficially similar-looking positions, the 1-5
backgame is a big pass, whereas the 2-5 backgame is no double.
================================================================
GNU Backgammon Position ID: 2G4DADb8vgcAAA
+24-23-22-21-20-19------18-17-16-15-14-13-+ O: gnubg
| O O O | | O O | 0 points
| O O O | | O O |
| O | | |
| | | |
| | | |
| X |BAR| |v (Cube: 1)
| X X | | |
| X X X | | |
| X X X | | |
| O O X X X | | | On roll
| O O X X X | | | 0 points
+-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: tchow
Double, take: 0.745
No double: 0.733 (-0.012)
Wbg Wg W L Lg Lbg
8.7 33.5 55.6 44.4 0.0 0.0
================================================================
GNU Backgammon Position ID: 2G4DADPmfQ8AAA
+24-23-22-21-20-19------18-17-16-15-14-13-+ O: gnubg
| O O O | | O O | 0 points
| O O O | | O O |
| O | | |
| | | |
| | | |
| |BAR| |v (Cube: 1)
| X | | |
| X X X | | |
| X X X | | |
| O X O X X X | | | On roll
| O X O X X X | | | 0 points
+-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: tchow
Double, take: 0.885
No double: 0.876 (-0.010)
Wbg Wg W L Lg Lbg
6.1 34.5 59.3 40.7 0.2 0.0
================================================================
GNU Backgammon Position ID: 2G4DABuP9w4AAA
+24-23-22-21-20-19------18-17-16-15-14-13-+ O: gnubg
| O O O | | O O | 0 points
| O O O | | O O |
| O | | |
| | | |
| | | |
| |BAR| |v (Cube: 1)
| | | |
| X X X | | |
| X X X X | | |
| X O O X X X | | | On roll
| X O O X X X | | | 0 points
+-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: tchow
Double, take: 0.810
No double: 0.788 (-0.022)
Wbg Wg W L Lg Lbg
2.9 39.2 57.1 42.9 0.2 0.0
================================================================
GNU Backgammon Position ID: 2G4DwDC2eTcAAA
+24-23-22-21-20-19------18-17-16-15-14-13-+ O: gnubg
| O O O | | O O | 0 points
| O O O | | O O |
| O | | |
| | | |
| | | |
| |BAR| |v (Cube: 1)
| | | |
| X | | |
| X | | X |
| O X X X O X | | X X | On roll
| O X X X O X | | X X | 0 points
+-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: tchow
Double, pass: 1.000
No double: 0.960 (-0.040)
Double, take: 1.388 (+0.388)
Wbg Wg W L Lg Lbg
1.9 26.2 75.6 24.4 0.9 0.0
================================================================
GNU Backgammon Position ID: 2G4DwBizeTcAAA
+24-23-22-21-20-19------18-17-16-15-14-13-+ O: gnubg
| O O O | | O O | 0 points
| O O O | | O O |
| O | | |
| | | |
| | | |
| |BAR| |v (Cube: 1)
| | | |
| X | | |
| X | | X |
| X O X X O X | | X X | On roll
| X O X X O X | | X X | 0 points
+-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: tchow
No double: 0.631
Double, take: 0.571 (-0.059)
Wbg Wg W L Lg Lbg
0.4 23.7 61.4 38.6 4.4 0.1
================================================================
--
Tim Chow tchow-at-alum-dot-mit-dot-edu
The range of our projectiles---even ... the artillery---however great, will
never exceed four of those miles of which as many thousand separate us from
the center of the earth. ---Galileo, Dialogues Concerning Two New Sciences
Walt
> Here's some information from Walter Trice's "Backgammon Boot Camp" to support
> the claim that the 2-5 backgame is actually quite good.
>
> Trice remarks that it's not too bad a rule of thumb to double a well-timed
> backgame when you have three points left in front of the more advanced
> anchor.
The thing is, I've often doubled already by the time I've reached this
position.. Backgames come about when the other player is really really
behind.
Interesting data.
//Walt
tc...@lsa.umich.edu
Walt <walt_...@SHOESyahoo.com> wrote:
>The thing is, I've often doubled already by the time I've reached this
>position.. Backgames come about when the other player is really really
>behind.
This is true, but the point of the positions is to demonstrate how much
equity the backgame player has even without cube possession.
David C. Ullrich
wrote:
Interesting and a half.
Backgammon Boot Camp is really an essential book.
>//Walt
>
David C. Ullrich
"Understanding Godel isn't about following his formal proof.
That would make a mockery of everything Godel was up to."
(John Jones, "My talk about Godel to the post-grads."
in sci.logic.)