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Backgammon => Backgammon problems => Topic started by: PersianLord on May 14, 2008, 10:46:24 PM

Poll
Question: Red to play 5-2
Option 1: bar/23-7/2 votes: 0
Option 2: bar/18 votes: 2
Option 3: bar/23-13/8 votes: 8
Option 4: bar/23-6/1 votes: 0
Option 5: none votes: 0
Title: Position #30
Post by: PersianLord on May 14, 2008, 10:46:24 PM
Position information:

Pip-count: Red 132-73 White
Score:       Red     5-4  White
Match:            7-pointer

(http://www.freewebs.com/persianlord/position30.png)

First make your choice and then read on.
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Spoiler
Red is in a very perilous position. With the cube on 2 and match to 7, he should really fear a gammon loss which will finish him off. So his #1 periority should be avoiding a gammon loss, not wishing desperately to get a late shot by staying. Thus he should simply and wisely, not cowardly, escape with bar/18 in hope of not getting hit next round and starting a hard, but possible gammon-saving project. Note that if he stays on the 2-pt, white will not hesitate to even hit loose, considering the red's weak home board and the great value of a gammon win, and this is apart from the fact that with 9 rolls white will be able to close out his board (2-2,4-2, 6-2, 3-3, 6-4, 6-6). Here is GNUBG's analysis:

    1. Cubeful 2-ply    bar/18                       Eq.:  -1.242
         3.6%   0.2%   0.0% -  96.4%  34.6%   0.1%

    2. Cubeful 2-ply    bar/23 13/8                  Eq.:  -1.295 ( -0.053)
         8.3%   0.9%   0.0% -  91.7%  50.8%   0.2%
       
    3. Cubeful 2-ply    bar/23 7/2                   Eq.:  -1.333 ( -0.090)
         8.5%   1.1%   0.0% -  91.5%  55.2%   0.2%
     
    4. Cubeful 2-ply    bar/23 6/1                   Eq.:  -1.399 ( -0.157)
         7.4%   0.9%   0.0% -  92.6%  60.1%   0.2%
   
Note that with bar/23-13/8, your chances of a win is 8.3% versus 3.6% if you play the best move (bar/18) but the key point is in the probability of the terrific gammon loss: 50.8% versus 34.6%.

But what about if this position occurs in a DMP game (or 1-pt match)?

Had this position been taken from a DMP game, it would have been a silly blunder to escape because it will nearly guarantee a loss which is not important whether be a single, a gammon or even a backgammon:

    1. Cubeful 2-ply    bar/23 13/8                  Eq.:  -0.847
         7.6%   0.5%   0.0% -  92.4%  39.6%   0.2%
       
    2. Cubeful 2-ply    bar/23 7/2                   Eq.:  -0.852 ( -0.005)
         7.4%   0.4%   0.0% -  92.6%  44.7%   0.2%
       
    3. Cubeful 2-ply    bar/23 6/1                   Eq.:  -0.865 ( -0.017)
         6.8%   0.4%   0.0% -  93.2%  49.4%   0.2%
       
    4. Cubeful 2-ply    bar/18                         Eq.:  -0.962 ( -0.115)
         1.9%   0.2%   0.0% -  98.1%  18.3%   0.0%
       

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Title: Re: Position #30
Post by: spielberg on May 15, 2008, 06:25:45 PM
Spoiler
Yaaay I got it right! I had to think quite a bit tho' and was probably prompted into recognising that it's an unusual sort of move for backgammon, generally a game which should be played aggressively, in which it's correct to be wimpish purely by Ali's selection of it as a problem.
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Title: Re: Position #30
Post by: PersianLord on May 15, 2008, 06:39:24 PM
Quote from: spielberg on May 15, 2008, 06:25:45 PM
Spoiler
Yaaay I got it right! I had to think quite a bit tho' and was probably prompted into recognising that it's an unusual sort of move for backgammon, generally a game which should be played aggressively, in which it's correct to be wimpish purely by Ali's selection of it as a problem.
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Spoiler
hmm......  :cool: 
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