Forum Archive : Jellyfish

Backgame play

From:   Brian Sheppard
Date:   19 February 1997
Subject:   Re: opening toughie
Google:   01bc1e75$9cefcf20$

JF's assessment of the backgame's potential is always too low. There
are several problems with JF's play in backgames that render its
judgments unsound.

First, JF plays the backgame side as though it were trying to win a race.
It will bury a man rather than expose a blot. It will hit the opponent, as
though it were possible to contain that man and win a priming game or race.
It will break its rearmost anchor so that a man is available at the edge of
the prime. If the backgame's timing is unsound, JF will not play to rectify

Second, JF does not hang onto its back points long enough. JF seems to play
to save the gammon, rather than win. This is not surprising, because...

Third, when JF does hit a shot, JF mishandles the containment situation.
JF does not build outer table primes, and it does not spread its checkers
at the proper distance. I think its technique is to bring men around to
launch an attack on the exposed man. This technique is not the worst
possible, but it loses equity in many cases because the chance of picking
up a second man is lost.

When I play backgames against JF, I have noticed that it handles the
blockading side badly, too.

First, JF will double a backgame too early. When you take into account
how badly it will play for the rest of the game, you can even beaver some
of its doubles.

Second, JF will always give a backgame adequate timing. You can always
leave another blot open, and JF will hit it if it is at all possible. If
it is impossible, JF will hang around, waiting to hit it. The net result
of this is that every back game against JF becomes an extreme backgame--
one that might lead to a position like #127.

Third, JF doesn't deliberately play to crunch your inner board. It focuses
on bringing its men in cleanly, which is a worthwhile goal, to be sure, but
much, much better is to force a crunch, and only then bring the men in.

Fourth, and this is the biggest mistake of all, when you double after
hitting a man you get an unexpected bonus: JF beavers, even if you have a
solid prime!

So I distrust JF rollouts in which backgames are prominent. Chances are
that the trailing side is being misjudged.
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Backgame play  (Brian Sheppard, Feb 1997) 
Bearoff database bug  (Vince Mounts+, May 1998) 
Cube strategy  (Fredrik Dahl, July 1995) 
Doubling at 2-away, 2-away  (Michael Bo Hansen, May 1998) 
JF tackles New Ideas in Backgammon  (Nigel Gibbions+, Mar 1998) 
Review of JF Player 3.0  (Geoff Oliver, Apr 1997) 
Review of JF Tutor 1.0  (John Bazigos, Feb 1995)  [Long message]
Showdown in Texas  (Chuck Bower, July 1997) 
Strengths and weaknesses  (Daniel Murphy, Jan 1998)  [Long message]
What is a Jellyfish?  (John S Mamoun, Dec 1996) 
Why the name?  (Fredrik Dahl, Dec 1996) 

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