Snowie

Forum Archive : Snowie

 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
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
```

### 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)