RE: [Bug-gnubg] Strange position

[Ian Shaw]

Hi Peter,

I think this is quite common. It's easy to find bearoff positions where
this is the case.


    GNU Backgammon  Position ID: CQAAEAEAAAAAAA
                    Match ID   : cAkFAAAAAAAA
    +24-23-22-21-20-19------18-17-16-15-14-13-+  O: O
OOO | O     O          |   |                  |  0 points
OOO |                  |   |                  |  
OOO |                  |   |                  |  
 OO |                  |   |                  |  
 OO |                  |   |                  |  
    |                  |BAR|                  |v (Cube: 1)
 XX |                  |   |                  |  
 XX |                  |   |                  |  
XXX |                  |   |                  |  
XXX |                  |   |                  |  Rolled 21
XXX |    X        X    |   |                  |  0 points
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: X

Cube analysis
4-ply cubeless equity  +0.108
  0.554 0.000 0.000 - 0.446 0.000 0.000
Cubeful equities:
1. Double, take         +0.111
2. Double, pass         +1.000  ( +0.889)
3. No double            +0.056  ( -0.056)
Proper cube action: Double, take


X should double and O should take.
If X fails to bear off both men, 0 should re-double and X should pass.

    GNU Backgammon  Position ID: AQAAJAAAAAAAAA
                    Match ID   : AQEAAAAAAAAA
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  O: O (Cube: 2)
OOO | O     O          |   |                  |  0 points
OOO |                  |   |                  |  On roll
OOO |                  |   |                  |  
 OO |                  |   |                  |  
 OO |                  |   |                  |  
    |                  |BAR|                  |^ 
 XX |                  |   |                  |  
XXX |                  |   |                  |  
XXX |                  |   |                  |  
XXX |                  |   |                  |  
XXX | X                |   |                  |  0 points
    +24-23-22-21-20-19------18-17-16-15-14-13-+  X: X

Cube analysis
2-ply cubeless equity  +0.889
  0.944 0.000 0.000 - 0.056 0.000 0.000
Cubeful equities:
1. Double, pass         +1.000
2. Double, take         +1.778  ( +0.778)
3. No double            +0.889  ( -0.111)
Proper cube action: Redouble, pass

Regards,
Ian Shaw
________________________________

        From: Peter Nikolov
        Sent: 11 February 2011 10:55
        To: address@hidden
        Subject: [Bug-gnubg] Strange position
        
        
        I wonder for the existence of any particular position(s), when
it is correct:   

        1. Player X to double, and player Y to take it. 

        Player X rolls next. Then, it is correct again: 

        2. Player Y to re-double, then player X to pass. 

          

        (If exists, most probably after step 1 X did play the worst
possible moves with the worst possible rolls. Obviously if X played the
best possible moves with the best possible rolls, then player Y must not
redouble! What about if X played the best with the worst dices?)