I'm analyzing positions for the incorrect pass needed percentage (i.e., you double in a position that is a No Double / Take and want to know how frequently the opponent must pass in order to make the double profitable.)

The numbers I'm getting in XG don't match with my calculations. I contacted XG support about this, but haven't heard a response. Does anyone else have some insight?

Example

http://imgur.com/a/WJAapB2

You see XG says villain must pass 13.1%. My calculations give 15.1%.

x = pass %


x(0.6177) + (1-x)(-0.11) = 0
x = 0.151


Thanks for any help.

Your calculation looks correct to me. The way I verified it is to assume Black passes 15.1% of the time. Then doubling makes your equity 1.000 15.1% of the time and 0.2724 (the D/T equity) 84.9% of the time:

0.151 * 1.000 + .849 * 0.2724

That equals .3823, the same equity as no double.

I'm guessing there's some other factor that XG is accounting for that we're not seeing, though the equivalent GnuBG number agrees with our way of calculating things.

Ooh -- it looks like XG, instead of doing --

.11 / (.6177 + .11)

(which is our calculation), it's doing --

.11 / (.6177 + .11 + .11)

Does it make any sense to do it XG's way? I don't see how.

Thanks for the feedback. What's interesting is there are some positions where I see XG is accurate according to this formula.

XGID=-A-cC-E-C---aB---b-cbbAb--:0:0:-1:00:0:0:0:5:10

X:X O:O

Score is X:0 O:0 5 pt.(s) match.

+13-14-15-16-17-18------19-20-21-22-23-24-+

| X O | | O O X O |

| O | | O O X |

| O | | O O X |

| | | O |

| | | O |

| |BAR| |

| | | |

| | | |

| | | X |

| O X | | X X X X |

| O X | | X X X O X |

+12-11-10--9--8--7-------6--5--4--3--2--1-+

Pip count X: 135 O: 115 X-O: 0-0/5

Cube: 1

X on roll, cube action



Analyzed in 3-ply

Player Winning Chances: 59.94% (G:20.60% B:0.40%)

Opponent Winning Chances: 40.06% (G:10.71% B:0.43%)



Cubeless Equities: No Double=+0.258, Double=+0.558



Cubeful Equities:

No double: +0.419

Double/Take: +0.328 (-0.090)

Double/Pass: +1.000 (+0.581)



Best Cube action: No double / Take

Percentage of wrong pass needed to make the double decision right: 13.5%

Think I screwed up trying to put that position that way. I'm a noob with these formats. Anyway, it feels like XG has a bug or something going on.

And no, I can't see a way that formula would make sense.

XG responded and it is indeed a bug they marked to fix quite a while ago. So, they're on that. Thanks for the response.