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Re: [Bug-gnubg] Effective pip count (EPC) bug


From: Christopher D. Yep
Subject: Re: [Bug-gnubg] Effective pip count (EPC) bug
Date: Fri, 05 Sep 2003 06:51:48 -0400

At 12:47 AM 9/5/2003 -0400, I wrote:
Windows XP, GUI version
version 0.14-dev 1.1345 030904
version 0.14-dev3D 1.1345 030904 [bug exists in both old and "3D" versions of gnubg]

Set-up the following position:

    GNU Backgammon  Position ID: /wAAAP4BAAAAAA
                    Match ID   : cAkAAAAAAAAA
    +24-23-22-21-20-19------18-17-16-15-14-13-+  O: gnubg
 OO | O                |   |                  |  0 points
 OO | O                |   |                  |
  O | O                |   |                  |
  O | O                |   |                  |
  O | 8                |   |                  |
    |                  |BAR|                  |v (Cube: 1)
  X | 8                |   |                  |
  X | X                |   |                  |
  X | X                |   |                  |
 XX | X                |   |                  |  On roll
 XX | X                |   |                  |  0 points
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  X: Chris

Then,

show onechequer

gnubg reports that each side has an EPC of 12.578 (and an avg. rolls (to bearoff) of 12.578/8.167 = 1.540). This is incorrect; the correct EPC is about 29.

Sorry, for some reason I mixed up "show onesidedrollout" with "show onechequer". So, gnubg is correctly reporting that the EPC for a single checker on the 8 point is 12.578. No bug here.

Also, the onechequer statistics reverses the players. The pips, Avg. rolls, Std. dev., EPC, and wastage numbers listed for player "gnubg" are actually those of player "Chris" and vice-versa (the above is a symmetric position, but change gnubg's position to 7 on the 1 pt. and 1 on the 2 pt. for example).

This is an actual bug in "show onechequer" however.

Also, "show onesidedrollout" reverses the Effective pip count numbers when player0 is on roll (if player1 is on roll the numbers are correct). For example:

    GNU Backgammon  Position ID: /wAAAP4CAAAAAA
                    Match ID   : MAEAAAAAAAAA
    +-1--2--3--4--5--6-------7--8--9-10-11-12-+  O: gnubg
 OO | O  O             |   |                  |  0 points
 OO | O                |   |                  |  On roll
  O | O                |   |                  |
  O | O                |   |                  |
  O | 7                |   |                  |
    |                  |BAR|                  |^ (Cube: 1)
  X | 8                |   |                  |
  X | X                |   |                  |
  X | X                |   |                  |
 XX | X                |   |                  |
 XX | X                |   |                  |  0 points
    +24-23-22-21-20-19------18-17-16-15-14-13-+  X: Chris

"show onesidedrollout" reports:

                        EPC             Wastage
Player gnubg            28.999          20.999
Player Chris            29.005          20.005

The correct numbers are (29.005, 20.005) and (28.999, 20.999) for gnubg and Chris respectively.

Chris





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