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Re: [Bug-gnubg] Bearoff database

From: Øystein Schønning-Johansen
Subject: Re: [Bug-gnubg] Bearoff database
Date: Thu, 12 Jan 2017 00:41:26 +0100

Really strange!
I have built a one sided database using GMP with fractions with my own piece of code. Since I use fractions from GMP there should be no rounding error. Here are my numbers for position index 47:

Index: 47
 0: 0
 1: 0
 2: 1/18
 3: 445/648
 4: 5939/23328
 5: 73/23328

These numbers agrees to the numbers GNU Backgammon. Can it really play this incorrectly? How does that happen?


On Sun, Jan 8, 2017 at 11:26 PM, Philippe Michel <address@hidden> wrote:
On Sun, 8 Jan 2017, isambard mews wrote:

I tried to recreate the bearoff database and noticed some differences which could be due to rounding, but already at position #47 there were some significant differences. My workings for position 47 are given below. Have I made a mistake in the calculation methodology?

Th discrepancy for position #47 is not a rounding error. The difference is 11/1296 more bearoffs in 2 rolls instead of 3 for gnubg.

Interestingly, the average number of rolls to bear off is 2.21382 for you and 2.20528 for gnubg but the race4 software there : http://www.bkgm.com/rgb/rgb.cgi?view+788 that works recursively and plays perfectly claims that the average is 2.117155, so it looks like gnubg misplays a dice in one situation and you do in two.

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