Snowie

Forum Archive : Snowie

 
Checker-play-according-to-score bug

From:   Peter Schneider
Address:   schneiderp@gmx.net
Date:   5 June 2001
Subject:   Cubeful rollout bug
Forum:   rec.games.backgammon
Google:   3b1ff47d$0$26420$64889074@news.comundo.de

Hi all,

Has anybody else had bugs related to cubeful Snowie rollouts? I have
useless results nearly every time. I think that the bug occurs only if

-- the rollout is 3-ply *cubeful*, cube 3-ply (the bug does not appear in
   cubeless rollouts, not sure about the 3-plies)

-- Some higher number of games are already performed in the rollout. The
   bug does sometimes not occur before a number of games are rolled out.
   This number seemed to vary but was always smaller than the necessary
   number of games.

The bug seems to be position independent; I have not found a way to avoid
it yet (other than un-checking the cubeful checkbox).

Anybody else?

Greetings,
Peter aka the juggler

Dean Gay  writes:

I seem to remember that one of the conditions necessary for the bug to
appear is that it be a FULL, not a truncated rollout. I'm not entirely
sure this is the case, but that's what I recall.

Christopher D. Yep  writes:

Hi Peter,

If you're using Snowie 3, I believe this problem specifically only
occurs when you perform a rollout with checker play according to score
(this specifically also means that you are performing a cubeful rollout,
otherwise this checkbox won't even be available).

Specifically sometimes the rollout will show one side winning gammons
when gammons are impossible.  Other times one side will be shown winning
*zero* gammons, when clearly gammons are possible (or even likely).

I don't often perform "checker play according to score" rollouts since
the rollouts take considerably longer than normal cubeful rollouts (with
checker plays based on cubeless money equity) without improving accuracy
very much.  However the general consensus among several users I have
talked to is that the overall *equities* are likely correct even though
the breakdown (backgammons, gammons, normal wins) is incorrect.

For example, here are the rollout results that you reported on June 7,
2001:

Rollout      Money equity: 0,399
               0,0%   6,0%  71,6%    28,4%   9,4%   0,0%
               95% confidence interval:
                  - money cubeless eq.: 0,399 0,007,
                  - live cube no redouble: 0,883 0,008,
                  - live cube redouble take: 0,851 0,009.

The above hypothesis states that the money cubeless equity is 0.399
despite the fact that the displayed numbers (0.0%, 6.0%, 71.6% 28.4%
9.4% 0.0%) actually imply a 0.415 money cubeless equity.  Similarly, the
hypothesis states that the 0.883 and 0.851 numbers are in fact valid.

One hypothesis is that Snowie always (accurately) keeps track of the
overall equity, but that there is some type of display flaw that causes
it to erroneously report some of the wins as gammons or vice-versa.
To test this hypothesis, run the same position *without* checking
"checker play according to score."  In the position that you posted on
June 7, 2001 (5-away/5-away with cube on 2), this will likely not make
much difference in the final results.  See if the equity comes close to
equity that Snowie reports with "checker play according to score."

Chris
 
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Snowie

Announcement  (Olivier Egger, Apr 1998) 
Checker-play-according-to-score bug  (Peter Schneider+, June 2001) 
Error rates  (Gregg Cattanach, Oct 2000) 
Hints and questions  (Achim Müller+, Aug 1998) 
Luck calculation  (Gregg Cattanach+, Dec 1999) 
Questions and answers  (David Montgomery, Dec 1998) 
Running in low priority  (lmfback+, Oct 2004) 
Snowie 4.0  (SnowieGroup Info, Oct 2002) 
Snowie 4.3 update  (Gregg Cattanach, July 2005)  [GammOnLine forum]
Snowie cube evaluation  (Kit Woolsey, Sept 2007)  [GammOnLine forum]
Snowie vs GNU  (Stanley E. Richards+, Oct 2005)  [GammOnLine forum]
Snowie vs. Jellyfish  (Mark Driver, Apr 2001) 
Snowie vs. Jellyfish  (Daniel Murphy, Oct 2000) 
Snowie vs. Jellyfish  (Gregg Cattanach+, Sept 2000) 
Snowie vs. Jellyfish  (Wayne Crookes, Jan 1999) 
Snowie vs. Jellyfish  (Kenneth M. Arnold+, May 1998)  [Long message]
Terminology  (Alexander Nitschke, Sept 1998) 
Using rollouts  (Michael J. Zehr+, Oct 1998)  [Long message]

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