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[Bug-gnubg] FW: Wrong luck adjusted result on Grandmaster analysis

From: Ian Shaw
Subject: [Bug-gnubg] FW: Wrong luck adjusted result on Grandmaster analysis
Date: Tue, 6 Jan 2015 09:21:10 +0000



From: Ian Shaw
Sent: 06 January 2015 09:16
Subject: RE: [Bug-gnubg] Wrong luck adjusted result on Grandmaster analysis


Hi Richard,


I don’t know much about the mEMG Luck Rate, I’m afraid – I’ve never given it any attention because I think MWC is a better measure of luck. However, since luck is normalised from MWC to mEMG, the conversion is affected by the cube value. I suspect that very lucky swings at higher cube values can show a lesser value when converted to mEMG. (Or maybe it’s the other way round, I’m not sure!)


I notice that 2 of tophat’s luckiest rolls, (66 on move 11, 55 on move 18) are on a 2-cube, so they may have different effect than the 66 on move 2, where the cube is at 1.


Gnubg reports EMG Total luck as (-0.642 and +1.791). That’s a 2.4 game swing, which looks like a lot of luck for a single game, consistent with the MWC report. Dividing by the number of moves (20, 19) gives the reported mEMG luck values of (-32.1, +94.3).


This all looks reasonable to me, but, as I said, I’m no expert on this area.


What would you expect to see in these circumstances? Do you have other examples?


n  Ian



From: RICHARD BEAGLEY [mailto:address@hidden]
Sent: 06 January 2015 08:30
To: Ian Shaw
Cc: address@hidden
Subject: Re: [Bug-gnubg] Wrong luck adjusted result on Grandmaster analysis




I monitor the mEMG luck differential - this case (-126.4) was the most adverse in my 383 (ignoring 1 point matches) results todate on DG (OK I'm new here).  My luck adjusted success rate todate is 66.5% cf 63.6% actual and I have had many results changed when luck adjusted.  This was an apparent glaring anomaly.


My chequerplay was Expert (v Beginner)

My Cube was Supernatural (v Awful)


Logic would say that I would probably have won if the luck distribution was less extreme.


Surely there is a flaw in your formula which says otherwise!






From: Ian Shaw <address@hidden>
To: RICHARD BEAGLEY <address@hidden>; "address@hidden" <address@hidden>
Sent: Monday, 5 January 2015, 14:17
Subject: RE: [Bug-gnubg] Wrong luck adjusted result on Grandmaster analysis


Hi Richard.


The luck adjusted result looks OK to me.


You had -12.342% luck and tophat had +35.705% luck.

The actual result was you -50%, tophat +50%.


The Luck-Adjusted result formula = Actual Result – Own Luck + Opponent’s Luck.


Your luck-adjusted result = -50 - -12.342 + 35.705 = -1.953%

Tophat’s luck-adjusted result = 50 – 35.705 + -12.342 = -1.953%


In other words, without the luck, tophat would have got to 1.95% instead of +50%, and you would have got to -1.95% instead of -50%. His victory was almost entirely by luck.


You aren’t the first person to find this confusing.


If the formula were instead (50 – Own Luck + Opponent’s Luck), we would have got 98.05% and 1.95% in your favour.


May be it’s the Actual Result that is the source of the confusion. If this were reported as +100 and 0, rather than +50 and -50, the current formula  (Result – Own Luck + Opponent’s Luck), would give 48.05% and 51.95%. This indicates that, with the luck removed, your opponent only managed to get from 50% to 51.95%. Again, his victory was almost entirely luck.


I think that  (50 – Own Luck + Opponent’s Luck) gives the most intuitive result.


Does anyone know how the other two active bots, XG and BgBlitz, report the luck adjusted result? It might be sensible to standardize on a definition and use that. I’ve a feeling that XG uses (50 – Own Luck + Opponent’s Luck), but this is only based on my hazy recollection of the discussions at DailyGammon when Miran ran some luck-adjusted tournaments.


n  Ian


From: bug-gnubg-bounces+address@hidden [mailto:bug-gnubg-bounces+address@hidden] On Behalf Of RICHARD BEAGLEY
Sent: 04 January 2015 16:08
To: address@hidden
Subject: [Bug-gnubg] Wrong luck adjusted result on Grandmaster analysis


Version GNU backgammon 0.90.0 Aug 8 2011


via XQuartz 2.7.7 (xoorg-server 1.15.2) on MAC OSX 10.6.8


Analysis - grandmaster 3 ply


This a single game result (3 point) with extreme differences in move, cube and luck ratings.  I should have had a luck adjusted win!


Is this a known bug and / or is my software out of date?




Richard Beagley (tregurtha)


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