Forum Archive : Rollouts

Level-5 versus level-6 rollouts

From:   Chuck Bower
Date:   20 August 1997
Subject:   Re: An endgame problem
Google:   5tfs86$6cj$

1) For rollouts, I go straight to level-6.  Occasionally I'll use level-5
(with cube) after adjusting the settlement limit based on the level-6
result. THEN I MAKE SURE that the level-5 cubeless results are consistent
with the (already completed benchmark) level-6 (cubeless).

> What do you mean by "*make sure* (they) are consistent"?  My level-5
> cubeless rollout result is not consistent with the level-6 rollout
> result, since three out of four plays go up by about .02, while the last
> one is up by .06.  It only tells me that there's a difference in the
> playing style between level 5 and level 6, and that I should trust the
> level 6 rollouts more when it comes to checkers play.  One problem is
> though that there's usually a cube somewhere in this game, and level 6
> doesn't know anything about that.

OK.  If the level-5 rollout isn't consistent with level-6 rollout, don't
believe level-5.  (By "consistent" I mean "statistically consistent".)  As
far as "knowing" about the cube, one of us may be confused (or maybe
neither) but here is the way I understand JF's checker play decisions:

   JF ASSUMES that the game is cubeless (always played to the end) and
   makes the play which maximizes equity in this case.  (Note that gammons
   count twice simple games, and backgammons thrice, and JF uses these

Human BG players sometimes think something like this:

   I have a legitimate cash (double, pass) next time if I make play A.
   Play B is probably better IF the game continues, but there are risks
   there that may allow a legitimate take (or even NO DOUBLE).  Go with the
   "safe" sure thing.  If my opp surprises me by taking, all the better!

To my knowledge, JFv3.0 does not use this kind of thinking.

Now the question arises "suppose I'm rolling out a CUBE position"
(that is, the question is Double or not, and/or drop or take).  Then it MAY
help to have JF use the cube.  BUT, Jellyfish only has a limited cube
algorithm in its rollouts, and these only at level-5 (inferior player).
"Limited" means that THERE CAN NEVER BE A TAKE.  If a side has access
to the cube AND is above the "settlement limit", then that sides scores
a simple win.  (NOTE:  there is an exception if a large swing has
occurred over the last 1296 dice chances AND there is a high enough
gammon chance.  This doesn't come up often and for this discussion can
be ignored.)

Here JF will roll the game out to the bitter end, but keep track of
FOUR SEPARATE SITUATIONS:  cubeless, centered cube, player on roll owns
cube, and player NOT on roll owns cube.  In the last three, the game is
"ended" when a player on roll has access to the cube AND is above the
settlement limit.  "Ended" just means the game is scored as a win for
that player, but the rollout ALWAYS continues until one side has 15
checkers off so that the "cubeless" statistics can be tabulated.

SO, if you first do a level-6 rollout, (adjust the "settlement
limit" if you so choose) and then do level-5 "limited cube" rollout, you
can compare the level-6 result with the level-5 CUBELESS result.  If

The fact is, you can use the level-6 cubeless result to determine
the proper CUBEFUL decisions (double/NO; drop/take), AND you can do it
for money play and match scores.  How do you do this?  You need to absorb
my previous posts.  It takes too long to explain right now.

> Another thing I do not adjust is the settlement limit.  I think it's only
> needed in short/long races and positions with high gammon rates (that
> equals about all positions now, doesn't it?), otherwise, about. 0.550
> will do nicely.  This is mainly because I do not know how to adjust it
> (shoot me if you like, but please tell me how I should do it while you
> kill me), and partly because I do not find it incredibly important.

I don't like to shoot good analysts.  (I don't even like shooting BAD
ones, but that may sometimes prove necessary....)  This "settlement limit"
thing is not a closed book, although Kit seemed to say that it was in a
post a couple weeks back.  Maybe I'm the only one getting my fingers
pinched, though...

My method of determining settlement limit has probably not been
posted.  Unfortunately I'm already late for dinner.  Let me get back to
that one.  But in short, I do a level-6 rollout, use those results and
match equities (if applicable) to find the settlement limit, tweek it
a bit (Bob Koca won't like this step!) and then plug it in to a level-5
limited cube rollout and go from there.  Stay tuned...

       c_ray on FIBS
Did you find the information in this article useful?          

Do you have any comments you'd like to add?     



Advice  (David Montgomery, Apr 1996)  [Long message]
Cautionary tale  (Kit Woolsey, Sept 1995) 
Combining rollouts  (Gregg Cattanach+, Dec 2003)  [GammOnLine forum]
Confidence intervals  (Bob Koca, Nov 2010) 
Confidence intervals  (Timothy Chow, May 2010) 
Confidence intervals  (Gerry Tesauro, Feb 1994) 
Cubeless vs centered-cube rollouts  (Ron Karr, Dec 1997) 
Duplicate dice  (David Montgomery, June 1998) 
How reliable are rollouts?  (David Montgomery, Aug 1999) 
Level-5 versus level-6 rollouts  (Michael J. Zehr, June 1998) 
Level-5 versus level-6 rollouts  (Chuck Bower, Aug 1997) 
Positions with inaccurate rollouts  (Douglas Zare, Oct 2002) 
Reporting results of rollouts  (David Montgomery, June 1995) 
Rollout settings  (Lokicol+, Apr 2010) 
Settlement limit  (Michael J. Zehr, Apr 1998) 
Settlement limit  (Kit Woolsey, Dec 1997) 
Settlement limit in races  (Alexander Nitschke, Dec 1997) 
Some guidelines  (Kit Woolsey, Apr 1996) 
Standard error and JSD  (rambiz+, Feb 2011) 
Standard error and JSD  (Stick+, Oct 2007) 
Systematic error  (Chuck Bower, Oct 1996) 
Tips for doing rollouts  (Douglas Zare, June 2002) 
Truncated rollouts  (Gregg Cattanach, Oct 2002) 
Truncated rollouts: pros and cons  (Jason Lee+, Jan 2006)  [GammOnLine forum]
What is a rollout?  (Gregg Cattanach, Dec 1999) 

[GammOnLine forum]  From GammOnLine       [Long message]  Long message       [Recommended reading]  Recommended reading       [Recent addition]  Recent addition

  Book Suggestions
Computer Dice
Cube Handling
Cube Handling in Races
Extreme Gammon
Fun and frustration
GNU Backgammon
Luck versus Skill
Magazines & E-zines
Match Archives
Match Equities
Match Play
Match Play at 2-away/2-away
Opening Rolls
Pip Counting
Play Sites
Probability and Statistics
Source Code
Strategy--Bearing Off
Strategy--Checker play


Return to:  Backgammon Galore : Forum Archive Main Page