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Re: [Bug-gnubg] Strange cube decision

From: Ned Cross
Subject: Re: [Bug-gnubg] Strange cube decision
Date: Sun, 27 Mar 2005 11:26:13 -0800
User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)

In general with these types of positions, the reason for the bot's ambiguous opinion is the fact that there is zero volatility. Whatever the correct decision is this turn, there is no sequence that will change it for next turn. In the example given, repeated rolls of 22 are the only thing bad that can happen for X, and O's situation does not change until X starts bearing off.

For the plies where GNU (incorrectly) thinks the winning % is in the lower end of the doubling window, GNU (correctly) sees no market losing sequences, hence the 'optional double'. My guess is that 4-ply says "no-double" instead of "optional double" because of slight round-off error.

Note that with deeper plies, (0->2->4) the win% (and hence the no-double or double/take equity) is creeping up as GNU gets closer to 'recognizing' the position.

For the plies where GNU (correctly) thinks the winning % is in the 80% range, the 1-ply look-ahead only sees that doubling is better then not doubling, but 3-ply see that doubling this roll really doesn't matter since it's still a double/pass next roll no matter what.

The analogous checker-play situation is when we see a bot make moves that seem counter-intuitive to us near the end of a game in a gin position. Since the bot (correctly) sees little or no equity difference, it makes apparently random moves.


Jim Segrave wrote:

Someone at dailygammon queried this gnubg analysis and I have to say
that I find the results a bit odd.

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