[Bug-gnubg] Effective Pip Count Bug

[Ned Cross]

I reported this minor bug back on 9/1, but I did not explain it very well.
I ran across the bug again today, so it still persists.

Running win32, old GUI, on Win2k, build 031122 (1.1457).

In some bearoff situations, the “One-Checker Race” window is getting the
pipcount for the 2 players swapped.  As a result the calculations for “Avg
rolls to bearoff”, “Effective Pip Count”, and “Estimated Cubeless GWC (blah
on roll):” are all reported incorrectly.

In the example I previously provided, the actual GWC for player on roll was
74.2% by 2-ply analysis, but GNU reported 47.2% in the theory window.
Details below.

I think Joern presented output from the no-gui version that showed correct
information, but the two examples below show an issue with the windows GUI
version.

The position I encountered today was similar, with the theory window giving
53.5% GWC instead of 71.3% (see below)

--Ned

The score (after 0 games) is: black 0, white 0 (match to 3 points)

Move number 41: X to play 63

 GNU Backgammon  Position ID: 1A0AAMkNAAAAAA
                 Match ID   : cAlvAAAAAAAA
 +13-14-15-16-17-18------19-20-21-22-23-24-+     O: black
 |                  |   | O  O  O  O       | OO  0 points
 |                  |   | O  O             | OO
 |                  |   |    O             | OO
 |                  |   |                  | O
 |                  |   |                  | O
v|                  |BAR|                  |     3 point match (Cube: 1)
 |                  |   |                  | X
 |                  |   |                  | X
 |                  |   |    X             | XX
 |                  |   | X  X             | XX  Rolled 63
 |                  |   | X  X     X     X | XX  0 points
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     X: white
Pip counts: O 34, X 31

* white moves 6/off 3/off
Alert: missed double ( -0.249)! [very bad]
Cube analysis
Rollout cubeless equity  +0.427 (Money:  +0.427)

Cubeful equities:
1. Double, take         +0.979
2. Double, pass         +1.000  ( +0.021)
3. No double            +0.730  ( -0.249)
Proper cube action: Double, take
Rollout details:
Centered 1-cube:
  0.713 0.000 0.000 - 0.287 0.000 0.000 CL  +0.427 CF  +0.730
 [0.000 0.000 0.000 - 0.000 0.000 0.000 CL   0.001 CF   0.002]
Player black owns 2-cube:
  0.717 0.000 0.000 - 0.283 0.000 0.000 CL  +1.144 CF  +0.979
 [0.000 0.000 0.000 - 0.000 0.000 0.000 CL   0.001 CF   0.002]
Truncated cubeful rollout (depth 11) with var.redn.

Output generated Tue Dec 02 14:15:37 2003
by GNU Backgammon 0.14-dev 1.1452 031119 (Text Export version 1.62)


Yet, under “Analyse/One-Checker Race/One Checker Bearoff” GNUBG gives:

Number of rolls to bear off, assuming each player has one chequer only.
                       Pips     Avg. rolls   Std.dev.
black                    31       4.370         1.019
white                    34       4.742         1.058
Estimated cubeless gwc (white on roll):  53.5332%


Effective pip count:
                       EPC      Wastage
black                  35.685    4.685
white                  38.725    4.725

EPC = Effective pip count = Avg. rolls * 8.167
Wastage = EPC - Pips

_______________________________________________________

black (O, 0 pts) vs. white (X, 0 pts) (Match to 5)

Game number 1

Move number 41: X to play 21

 GNU Backgammon  Position ID: 6B4AALJ1AAAAAA
                 Match ID   : UQmlAAAAAAAA
 +13-14-15-16-17-18------19-20-21-22-23-24-+     O: black
 |                  |   | O  O  O          | OO  0 points
 |                  |   | O  O             | OO
 |                  |   | O  O             | O
 |                  |   | O                | O
 |                  |   |                  | O
v|                  |BAR|                  |     5 point match
 |                  |   |                  | X
 |                  |   |                  | X
 |                  |   | X                | X
 |                  |   | X     X  X       | X   Rolled 21
 |                  |   | X  X  X  X     X | XX  0 points
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     X: white (Cube: 2)
Pip counts: O 43, X 38

* white moves 6/4 1/off
Alert: missed double ( -0.170)! [very bad]
Cube analysis
2-ply cubeless equity  +0.483 (Money:  +0.483)
  0.742 0.000 0.000 - 0.258 0.000 0.000
Cubeful equities:
  2-ply cubeful 100% speed [world class]
1. Double, take         +0.981
2. Double, pass         +1.000  ( +0.019)
3. No double            +0.811  ( -0.170)
Proper cube action: Redouble, take

Yet, under “Analyse/One-Checker Race/One Checker Bearoff” GNUBG gives:

Number of rolls to bear off, assuming each player has one chequer only.
                       Pips     Avg. rolls   Std.dev.
black                    38       5.230         1.123
white                    43       5.842         1.197
Estimated cubeless gwc (white on roll):  47.2289%


Effective pip count:
                       EPC      Wastage
black                  42.712    4.712
white                  47.712    4.712

EPC = Effective pip count = Avg. rolls * 8.167
Wastage = EPC - Pips