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Re: [Bug-gnubg] Errors in evaluation of races with backgammons

From: Joseph Heled
Subject: Re: [Bug-gnubg] Errors in evaluation of races with backgammons
Date: Mon, 27 Feb 2012 19:33:08 +1300

On 27 February 2012 19:09, Philippe Michel <address@hidden> wrote:
> On Mon, 27 Feb 2012, Joseph Heled wrote:
>> clearing checkers from the back is not the same as bearoff - you *can*
>> move any checker you want.
> Embarrassing. You're right of course and in my example 3s and 4s can
> certainly be played in a different way than in a bearoff.

An easy mistake to make. Still ....

Using some python trickery it is possible to get the true backgammon
figure. "true" here means that you always make the optimal move which
minimises the probability of backgammon.  The number is 40615026 /
(36^5) = 0.6716982730973429

Now, nngnu gives those numbers for plies 0 to 5

 0ply  0.6775242686271667
 1      0.6775177717208862
 2      0.6775177717208862
 3      0.6775176525115967
 4      0.6717002391815186
 5      0.6716980934143066

which I am happy about, but it seems that *there is* some problem in
gnubg, which gives different numbers for different plies.

I think someone should take a good look at this!


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