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

[Ian Shaw]

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


Regards
Ian Shaw