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BGonline.org Forums
Handicap Backgammon. One start with cube.
Posted By: Rick Janowski In Response To: Handicap Backgammon. One start with cube. (mochy)
Date: Wednesday, 21 January 2015, at 12:40 a.m.
Edge in Start Position (XG vs XG)
The edge can be calculated from equation (5) of my paper “Take-Points in Money Games”:
Cube-owned Equity Eo = CL*{p*(W+L+0.5*x)-L}, where:
CL = cube-level, or stake-level
p = cubeless win probability
W = Average value of Win
L = Average value of Loss
x = Cube-Ownership value.
In the opening position, where both sides can start, p = 0.0, and W = L, allowing the equation to simplify to: Eo = CL*x/4
The player holding a theoretical 1-cube is x/4 which equates to about 0.175, assuming x has the typical value of 0.7.
I checked this another way by considering XGR++ evaluated equities for each of the 21 opening rolls with either side starting and averaging for each roll and then averaging overall (these equities assume the player holds a theoretical 1-cube):
Eo = 0.1825 (ranging from 0.1813 to 0.1841)
This equates to an x-value of 0.73, incidentally.
PR-edge required for Fair-settlement
Using Xavier’s equation of Eo (holding 1-cube) = ppg = 0.066*PR-edge,
Fair settlement, PR-edge = 0.1825/0.066 = 2.77
With a PR-edge of 3, the player will be a small equity favourite with an expectation of about 1 point in every 66 games.
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