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RE: [Bug-gnubg] Fwd: An important link and a question about using EPC va

From: Ian Shaw
Subject: RE: [Bug-gnubg] Fwd: An important link and a question about using EPC values in deciding cube actions
Date: Fri, 4 Feb 2011 14:07:39 -0000

Hi Adi,
Gnubg doubling decisions are based on Rick Janowksi's theory, which I don't think any human would want to replicate over the board.
Gnubg does not use the epc or any other adjusted pip-count method, which are intended for humans. These are included purely for humans to use as a study aid.
The best information I have on epc is in Walter Trice's Backgammon Boot Camp, which is derived from his articles at Gammon Village. There are further articles at GV by Trice and by Douglas Zare  that expand on the information found in Boot Camp. Thanks for the link to Joachim's paper, which I'll enjoy reading. I haven't read it yet, so I can't tell whether it adds new information, or summarizes what is already known - a valuable thing in itself.
Trice explains that there is no general formula applicable to all situations. This is because the epc only tells you the average rolls to bear off, but not the amount of variance. If one player is stacked, a 65 is about as good as a 21, so there is less variance involved. This effect tends to help the leader, because the trailer is relying on the variance swings to catch up in the race. This means that for equal epc races, the trailer is better off in "pips vs. pips" races". So. although there is no universal formula, there are different rules that can be applied depending on whether the nature of the race is "pips vs. pips", "pips vs.. rolls" or "rolls vs. rolls".
Note to developers:
It might be a nice touch if Trice's formulae were added to the gnubg race theory tab. It could possibly replace the 8-9-12 rule, which applies in similar situations but is less accurate.
-- Ian


From: address@hidden [mailto:address@hidden On Behalf Of Adi Kadmon
Sent: 04 February 2011 13:45
To: address@hidden
Subject: [Bug-gnubg] Fwd: An important link and a question about using EPC values in deciding cube actions

Oops sorry I forgot to put the link in the last delivery. It's http://home.arcor.de/joachimmatussek/BearoffGWC.zip

- Adi

---------- Forwarded message ----------
From: Adi Kadmon <address@hidden>
Date: Fri, Feb 4, 2011 at 3:42 PM
Subject: An important link and a question about using EPC values in deciding cube actions
To: address@hidden

Hello all,
(1) As a sequel to a correspondence some months ago, here is a link for downloading Joachim Matussek's important article about an approximation-formula for EPC values and their use in cube decisions in bearoff positions. This time it's the original article, and in English - not just some section about it in a later article by someone else and moreover in the Danish language.

(2) I'd like to ask if there is at present a general formula for deciding cube decisions in bearoff positions after the correct EPC values are already given. I mean, does GNU make some particular computation on the EPC values it extracts using its data-bases? For instance, let's say  Black has a raw pip count of 57 and EPC=65.41, and White has a raw pip count of 60 pips and EPC=70.55, and it's White's roll. Does GNU use a certain "formula" with these figures in order to reach its evaluation of the correct cube decision? If so, does GNU use the same formula in any position whatsoever, or is a different variant of a formula needed for each different type of positions?
    Anyway, even if GNU does not use such formula(s), what are the current most modern approximation formulas (given already the exact EPC values) for humans to use?
-- Adi

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