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Is bot analysis of manually altered positions reliable?

Posted By: Karol Szczerek
Date: Saturday, 31 October 2015, at 7:18 p.m.

The neural network learns by playing extended number of games from starting position. This means that some positions, that we create manually as variants could be misanalyzed by a bot, because of an extremely low chance of occuring in a legal play.

A quick illustration could be a pair of positions below. First one is reachable by standard play:





White is Player 2

score: 0
pip: 152
Unlimited Game
Jacoby Beaver
pip: 157
score: 0

Blue is Player 1
XGID=-aa-BBC-A---bE--ae-e----B-:0:0:1:00:0:0:3:0:10
Blue on roll, cube action?

It has been reached after bottom player starts: 31P-54D-42P-51S. Bot says it's a borderline aggressive double:

Analyzed in XG Roller++ No double Double/Take
Player Winning Chances: 64,66% (G:24,65% B:1,41%) 64,61% (G:25,69% B:1,46%)
Opponent Winning Chances: 35,34% (G:9,33% B:0,49%) 35,39% (G:9,13% B:0,48%)
Cubeless Equities +0,456 +0,935
Cubeful Equities
No double:+0,666 (-0,014)
Double/Take:+0,680
Double/Pass:+1,000 (+0,320)
Best Cube action: Double / Take

Now let's create a manual alteration, and move bottom player's checker from the 8 to 9pt. That's a position, that has an extremely low probability of occuring, at best.





White is Player 2

score: 0
pip: 152
Unlimited Game
Jacoby Beaver
pip: 158
score: 0

Blue is Player 1
XGID=-aa-BBC--A--bE--ae-e----B-:0:0:1:00:0:0:3:0:10
Blue on roll, cube action?

eXtreme Gammon Version: 2.19.208.pre-release

In this position, bot's analysis is likely to be off, since it probably never were in an early game situation like this, with full stack on midpoint and a blot on the 9pt. instead of the 8pt, simultaneously.


Analyzed in XG Roller++ No double Double/Take
Player Winning Chances: 63,94% (G:24,17% B:1,35%) 64,02% (G:24,79% B:1,40%)
Opponent Winning Chances: 36,06% (G:9,66% B:0,57%) 35,98% (G:9,67% B:0,57%)
Cubeless Equities +0,432 +0,880
Cubeful Equities
No double:+0,635
Double/Take:+0,618 (-0,017)
Double/Pass:+1,000 (+0,365)
Best Cube action: No double / Take
Percentage of wrong pass needed to make the double decision right: 4,2%

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