Re: [Bug-gnubg] Analyse -> Market Window question?

[Ian Shaw]

Hi Wayne, 

The double point of the market window is the lowest winning chance at which you 
could consider a double. If this were the last roll of the game, and you would 
never get a chance to double later, it would be correct to double. 

In most circumstances, you should wait until you are nearer the Cash Point to 
double. If you double now, with about 55% winning probability, there is a good 
chance that things may go badly for you, and now it is only your opponent who 
has access to the cube. 

If you want to know more about doubling theory, try www.bkgm.com., for example 
http://www.bkgm.com/articles/GOL/Oct99/hanka99.htm

This isn't really a forum for position analysis, but I'll give yours a try.

In your position, both sides have an anchor on the 20-point, and the race is 
even. A classic reference position for a 20-point holding game would be for one 
side to have an anchor, the other side to have escaped his back men to the 
midpoint and have a 20-pip lead in the race. This would be a double and take. 

(You'll need to use a fixed width font such as Courier New to see the board 
position properly.)

    GNU Backgammon  Position ID: 2G7BAQOYnwcHAA
                    Match ID   : cAkAAAAAAAAE
    +24-23-22-21-20-19------18-17-16-15-14-13-+  O: White
    |          O  O  O |   | O  O           X |  0 points
    |          O  O  O |   | O              X |  
    |                O |   |                X |  
    |                  |   |                  |  
    |                  |   |                  |  
    |                  |BAR|                  |v (Cube: 1)
    |                6 |   |                  |  
    |                X |   |    X             |  
    |                X |   |    X           O |  
    |          X  O  X |   |    X           O |  On roll
    |          X  O  X |   |    X           O |  0 points
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: Blue


Cube analysis
2-ply cubeless equity  +0.5069
  0.7478 0.0258 0.0002 - 0.2522 0.0144 0.0003
Cubeful equities:
1. Double, take         +0.8423
2. Double, pass         +1.0000  ( +0.1577)
3. No double            +0.7936  ( -0.0487)
Proper cube action: Double, take

You can see that you have some work to do to get to my reference position; you 
must roll high and well to escape both back men and your opponent gets nothing 
much. Roughly speaking, since you need to roll 55 or 66 to get into a position 
where you can offer your opponent a borderline take/pass cube, you can't really 
have a double now.

I hope this helps.

-- Ian

From: address@hidden [mailto:address@hidden On Behalf Of Wayne Joseph
Sent: 06 June 2013 19:05
To: address@hidden
Subject: [Bug-gnubg] Analyse -> Market Window question?

Hallo all,

I am sorry for the new n00b question.

Please can anybody explain to me how the 'Analyse -> Market Window' function 
works?

In the screenshot below, I thought I offered a fairly decent cube, I held both 
5-points and had a little, but handy, 4-prime going.
The score was 0-0 (7-away, 7-away) and I was only 3 pips down in the race.

The Market Window function for me is very confusing (disregarding how 
relatively strong my position looked over the board). 
In the yellow highlighted line of the first screenshot below it says my cube 
market window opens up at 50.286% so I think it was correct to cube once I got 
above this?

After analysis, gnubg said my cube action was 'Very Bad' but I was around 55.7% 
to win the game at this point?

Can anybody explain why I am misunderstanding this feature?

Position ID: NM/BAQawt8EBAw
Match ID: cAngAAAAAAAE