Re: [Bug-gnubg] Optional redouble, or is it automatic

[Jim Segrave]

On Mon 09 Sep 2002 (11:10 +0100), Ian Shaw wrote:
> Why is this type of position called an "optional redouble"? Surely the
> redouble is automatic. I guess the 2-ply analysis is looking ahead and
> automatically doubling on the next roll so it sees no loss of equity.
> 
>     GNU Backgammon  Position ID: 2W4AAGdsbRMBGA
>                     Match ID   : AgGgAAAAEAAA
>     +-1--2--3--4--5--6-------7--8--9-10-11-12-+  O: mlp (Cube: 4)
>     |    X  O  O  O  O |   | O  O     O       |  0 points
>     |    X  O  O     O |   | O  O             |  On roll
>     |    X             |   |                  |  
>     |                  |   |                  |  
>     |                  |   |                  |  
>     |                  |BAR|                  |^ 5 point match
>     |                  |   |                  |  
>     |                  |   |                  |  
>     |             X    |   |                  |  
>     |    O  X  X  X  X | X |                  |  
>     | X  O  X  X  X  X | X |                O |  2 points
>     +24-23-22-21-20-19------18-17-16-15-14-13-+  X: ian
> 
>               Win     W(g)    W(bg)   L(g)    L(bg)   Equity  (cubeful)
> static:       0.158   0.057   0.002   0.494   0.053   (-0.647  (-0.579))
>  1 ply:       0.183   0.070   0.004   0.488   0.035   (-0.588  (-0.513))
>  2 ply:       0.151   0.054   0.003   0.509   0.047   (-0.662  (-0.596))
> 
> 
> No redouble         : -0.596
> Redouble, pass      : +1.000   (+1.596)
> Redouble, take      : -0.596   (+0.000)
> 
> Correct cube action: Optional redouble, take
> 
> 0-ply evaluation gets it right and calls it a missed double.
> 
> Alert: missed double ( -0.022)!
> Cube analysis
> 0-ply cubeless equity  -0.647
>   0.158 0.057 0.002 - 0.842 0.494 0.053
> 1. Double, take         -0.579
> 2. Double, pass         +1.000  ( +1.579)
> 3. No double            -0.601  ( -0.022)
> Proper cube action: Redouble, take

Odd - using today's build with evaluation set to world-class++ for
chequer and cube play I get the following evaluation:

Evaluator:      CONTACT

Input                   Value                            dE/dI
[snip]

                                Win                                      W(g)   
W(bg)   L(g)    L(bg)
                                Equity  (cubeful)
static:                 0.876   0.588   0.046   0.034   0.001   (+1.130         
(+1.186))
 1 ply:                 0.912   0.599   0.059   0.014   0.000   (+1.210         
(+1.251))
 2 ply:                 0.888   0.576   0.051   0.022   0.001   (+1.146         
(+1.201))

No redouble         : +1.201
Redouble, take      : +1.347   (+0.146)
Redouble, pass      : +1.000   (-0.201)

Correct cube action: Too good to redouble, pass

Which, to my untrained eye looks far more reasonable.

-- 
Jim Segrave           address@hidden