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Re: [Bug-gnubg] Confused

From: Ian Shaw
Subject: Re: [Bug-gnubg] Confused
Date: Fri, 12 Jun 2015 10:34:14 +0000

Hi Lucas, 

I agree that it is unwise to make assumptions.

I'd be surprised if just 3000 5-point matches (maybe 12000 games) was 
sufficient to produce statistical significance. I no longer have the results, 
but when I tested 0-ply vs 2-ply over 100000+ games, 2-ply was definitely 
ahead. I'm convinced it plays better.

I agree that 3-ply might not be better than 2-ply, due to odd vs. even ply 
evaluation effects. Michael Depreli's tests 
http://www.bkgm.com/articles/Keith/DepreliBotComparison/ showed that 3-ply had 
slightly better chequer play then 2-ply, but over-valued the doubler's 
position. This resulted in numerous wrong doubles and wrong takes.

If I recall correctly, 3-ply chequer play with 2-ply cube was in vogue for 
rollouts for a while. 

-- Ian

-----Original Message-----
From: Lucas [mailto:address@hidden 
Sent: 12 June 2015 10:35
To: Ian Shaw; address@hidden
Subject: Re: [Bug-gnubg] Confused

Hi Ian

To say that gnubg expert level plays less then worldclass or makes mistakes 
might not be true I did run on local disk expert against worldclass 1000 5 
point matches the result was worldclass  had a winrate of 50,2 % . To me that 
0,2 % might be due to luck.
I agree that expert plays sometimes a different move compared with worldclass 
on the same position etc

Assuming that a higher level of gnubg wil play better then lower level is not 
Last year i tested using Fibs,( were i did in the past 8 bots), 2 bots one set 
to play Worldclass and the other at grandmaster so 2 ply against 3 ply they 
played 3000 5 point matches Worldclass the lesser setting had a winrate of 55 % 
I mailed about it with Micheal Petch one of the maintainers of gnubg and he 
confirmed that indeed worldclass plays better the Grandmaster



-----Oorspronkelijk bericht-----
From: Ian Shaw
Sent: Thursday, June 11, 2015 6:22 PM
To: Michael Brennan ; address@hidden
Subject: Re: [Bug-gnubg] Confused

Hi Michael,

Welcome to GNU Backgammon.

1) Dice are no respecter of ability! Even the best players can be defeated by 
bad rolls. Look at the Luck ratings to see how gnubg thinks it played out.

Gnubg thinks it made no errors because it is using itself as the best judge of 

If you ask gnubg to play on Expert Level but analyse on World Class, you will 
start to see some errors creep into its game.

2) It depends on how beginnerish you are.

According to the FIBS Rating Calculator at 
http://www.netadelica.com/bg/fibscalc.html a player with a 500 point Elo 
advantage should win a 13-point match about 89% of the time. This increases to 
93% for a 21-pointer.

You can play with the calculator yourself for other scenarios. (The experience 
fields should be set to at least 400 for both players.)

I hope this helps.
Ian Shaw

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of Michael Brennan
Sent: 11 June 2015 00:19
To: address@hidden
Subject: [Bug-gnubg] Confused

I would be obliged for some help on the following. Please forward it on to 
someone who could answer if it arrives at the wrong destination.

gnubg describes my ability as a “beginner" - fair comment. However in a 13pt 
match, I beat gnubg 13-6. The analysis described gnubg’s ability as 
“supernatural" and indicated that it made no errors.

I Have two queries in relation to this

1. How come gnubg lost?

2. How many points should a match be in order to ensure that gnubg wins every 
time against a beginner?


Michael Brennan
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