[Bug-gnubg] Cube eval going crazy on this one

[Massimiliano Maini]

Hi all,

on bgonline this cube decision has
been posted and the evals returned by gnubg
are crazy on even ply:

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

The original one was in ma match, with
score 9aw-9aw: I changed it to money
to simplify since it doesn't make any
difference.

Cube analysis
0-ply cubeless equity  +0.190
  0.610 0.000 0.000 - 0.390 0.027
0.003
Cubeful equities:
1. No double        
   +0.398
2. Double, pass      
  +1.000  ( +0.602)
3. Double, take      
  +0.116  ( -0.282)
Proper cube action: No redouble, take
(31.9%)

Cube analysis
1-ply cubeless equity  +0.464
  0.747 0.000 0.000 - 0.253 0.027
0.003
Cubeful equities:
1. Double, take      
  +0.756
2. Double, pass      
  +1.000  ( +0.244)
3. No double        
   +0.695  ( -0.062)
Proper cube action: Redouble, take

Cube analysis
2-ply cubeless equity  +0.245
  0.637 0.000 0.000 - 0.363 0.026
0.003
Cubeful equities:
1. No double        
   +0.462
2. Double, pass      
  +1.000  ( +0.538)
3. Double, take      
  +0.244  ( -0.218)
Proper cube action: No redouble, take
(28.9%)

Cube analysis
3-ply cubeless equity  +0.503
  0.765 0.000 0.000 - 0.235 0.025
0.003
Cubeful equities:
1. Double, take      
  +0.844
2. Double, pass      
  +1.000  ( +0.156)
3. No double        
   +0.796  ( -0.048)
Proper cube action: Redouble, take

Cube analysis
4-ply cubeless equity  +0.288
  0.658 0.000 0.000 - 0.342 0.025
0.003
Cubeful equities:
1. No double        
   +0.532
2. Double, pass      
  +1.000  ( +0.468)
3. Double, take      
  +0.342  ( -0.189)
Proper cube action: No redouble, take
(28.8%)

Position ID:        XgAAILftgAARAA
Match ID:        AQEAAAAAAAAA
Evaluator:        
Crashed
        Win  
  W(g)    W(bg)   L(g)    L(bg)   Equity
   Cubeful  
static: 0.610   0.000   0.000
  0.027   0.003    +0.190    +0.398  

 1 ply: 0.747   0.000  
0.000   0.027   0.003    +0.464    +0.695
  
 2 ply: 0.637   0.000  
0.000   0.026   0.003    +0.245    +0.462
  
 3 ply: 0.765   0.000  
0.000   0.025   0.003    +0.503    +0.796
  
 4 ply: 0.658   0.000  
0.000   0.025   0.003    +0.288    +0.532
  


Cubeless winning chances swing a lot
between even and odd plies, while
gammon and backgammon percentages are
very stable.
Notice that even W% increase 0/2/4ply,
but so do odd ones 1ply/3ply.

Can we still blame this on odd-even
effect ?

MaX.

P.S.
The thread on bgonline is this one:

http://www.bgonline.org/forums/webbbs_config.pl?noframes;read=35362

Neil said that it wasn't worth to do
a 2ply cube rollout since the results
would be garbage, due to the fact 2ply
eval screws this position big time.
However, the (stopped) rollout 2ply
chequer/2ply cube gave the same result
as the (stopped) rollout 2ply chequer/3ply
cube and both were similar to 3ply
eval. Rollout/eval figures are in this
post:

http://www.bgonline.org/forums/webbbs_config.pl?noframes;read=35416