Re: [Bug-gnubg] Bearoff dB position, few questions

[Misja Alma]

Here's an example of a position that has different GWC depending on
the matchscore:

 GNU Backgammon  Position ID: 23YHAEC/AQAAAA
                 Match ID   : 8AllACAACAAA
 +13-14-15-16-17-18------19-20-21-22-23-24-+     O: gnubg
 |                  | O | O  O  O  O  O  O |     2 points
 |                  |   | O  O  O  O  O  O |
 |                  |   | O  O             |
 |                  |   |                  |
 |                  |   |                  |
v|                  |BAR|                  |     3 point match (Cube: 1)
 |                  |   |                6 | X
 |                  |   |                X | X
 |                  |   |                X | X
 |                  |   |             X  X | XX  Rolled 21
 |                  |   |             X  X | XX  1 point
 +12-11-10--9--8--7-------6--5--4--3--2--1-+     X: misja

I hope it is still readable :)
The point is that O is on the bar and X is bearing off:
At the given score, trailing 1-2 crawford, X should sacrifice about
13% winning chances to win 14% extra gammons and play 2/off 1/off.
Would the score have been 2-2 then X should of course play safe, for 100% GWC

Misja

On Fri, Jun 26, 2009 at 4:35 PM, Massimiliano
Maini<address@hidden> wrote:
>
> address@hidden wrote on 26/06/2009
> 15:34:56:
>
>> About the side question (purely theoretical):
>>
>> I think that there are many different equities and winning chances
>> implied in match play. If we want to keep things clear, the GWC
>> ***should *** not depend on the score. What has the match score to
>> do with the possibilities that a given position leads or not to
>> winning the game where it occurs? Clearly nothing.
>> It is absolutely necessary here to distinguish between Match Winning
>> Chance (win or loose) and Game Winning Chances (win/loose
>> simple, gammon, backgammon).
>
> Win/lose may be the same across different scores, but for sure gammon
> and backgammon percentages are not.
>
>> I would find it ***very*** helpful, at least for a beginner like
>> myself that would also like to have a theoretical perspective on
>> the game and/or software, if in the different dialog boxes of GnuBG,
>> it had been made explicit whether, in match play, the term
>> “equity” refers to match equity or the current game equity (as if it
>> were a money game). Currently my understanding is that money
>> game equity is completely irrelevant to match play, and that in a
>> match situation, in every window, the term equity refers to match
>> equity (even if expressed as NEMG), except when explicitly otherwise
>> mentioned.  Am I wrong about this?
>
> For match, the real thing is MWC.
> Conversion of MWC into EMG equities is done only for the purpose of
> providing an estimation of the magnitude of the gap betwen two plays
> in a manner that it is as independent as possible from the match score.
>
> A 1% MWC error at 0-0 to 15 could easily be a 10% error at double match
> point. On the other hand, the normalization to EMG equities will make
> the two errors similar in magnitude.
>
> MaX.
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