Snowie

Forum Archive : Snowie

 Questions and answers

 From: David Montgomery Address: monty@cs.umd.edu Date: 8 December 1998 Subject: Re: Questions about Snowie Error Rates Forum: rec.games.backgammon Google: 74iqd4\$27d@krackle.cs.umd.edu

```Vince Mounts writes:
> 1) I get _Move Error Rate_ as a percentage. What is this a percentage
>    of?

Nothing.  It isn't a percent of anything.

I believe that it's the average normalized gammon- and backgammon-price
adjusted total cubeless error per 100 unforced moves.

Unpacking this:
- it's a cubeless error rate.  The cube doesn't enter into it in any way.
- it's gammon- and backgammon-price adjusted.  Snowie uses its
match-equity table and the current cube level to calculate the gammon
and backgammon prices, and uses these rather than the money values.
- it's normalized.  An error that costs you the equivalent of the value
of 100% of a plain win is an error of size 1 -- regardless of the size
of the cube or the match score.
- it's the average of this per 100 unforced moves.

Basically, if you defined the error threshold as 0.0 and then went
through and added up all your errors in a match (add up the figures
in parentheses), divided by the number of unforced moves and multiplied
by 100, you would have it.

> 4) What is variance reduction. Why should I believe snowie when it says
>    my 288 game roll out is like 30000 games? What is it doing to get
>    the "extra" games?

Take a look at the Backgammon Galore newsgroup archive, Programming
Section.  There are several articles on variance reduction, although
they are somewhat technical.

If you have rolled out a complete game on 2- or 3-ply, you can
trust the number of equivalent games.  If you have truncated, especially
after only a few ply, you should regard the rollout as a little less
reliable than the equivalent games says.

David Montgomery
monty@cs.umd.edu
monty on FIBS
```

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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)
Snowie cube evaluation  (Kit Woolsey, Sept 2007)
Snowie vs GNU  (Stanley E. Richards+, Oct 2005)
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)
Terminology  (Alexander Nitschke, Sept 1998)
Using rollouts  (Michael J. Zehr+, Oct 1998)

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