| Score: Black needs 3, White needs 2 | ||||
| Play A |
Black to play 2
Candidate Plays Equities 22/20 +1.000 7/5 +0.950 5/3 +0.942 |
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Black, who rolled 3-2, has entered with a 3 and has a 2 to play. The three choices are to move the builder to the 3 point, stack on the 5 point, or come up to the 20 point.
Elliott Winslow did only a short rollout using JF 2.02 (seed 32, 1296 games, settlement 0.550), for respective Black equities of +0.942, +0.950, and +1.000, but apparently there were longer rollouts with similar data. Such data "prove" that Black's best play with the deuce is to come up to the 20 point!
How can this be? Doesn't Black want to pick up a second checker? Easing the gammon pressure on White flies in the face of logic. Can it really be that Black loses so many games cracking his six-prime through awkward sequences (allowing White ace followed by 6)?
Without having watched JF play, I speculate; but I strongly suspect the answer is that it misplays -- it does not maximize gammons by leaving the ace point slotted for Black after hitting there. JF just has Black close White out at the first available opportunity.
If so, JF will lose out on a plethora of gammons, and naturally will support the play that wins a tad more games. Coming up to the 20 point will rate best because Black will never get trapped. Stacking on the 5 point will rank second because it doesn't risk 4-3 and 4-4 cracking when White keeps the bar point.
At the table, Black chose to slide to the 3 point. Perhaps stacking is a hair better, perhaps it isn't. Black risks losing to more nightmare sequences, but hits on the ace point more often, which, with correct play, should lead to an increased gammon percentage.
[It is conceivable that coming up to 20 is correct anyway because the improved 7-5 distribution of the spares is more important for recirculation than staying back on the 22 is valuable in the short term. In this case, JF would luck out, getting the right answer for the wrong reason. In other words, if JF chooses coming up to 20 over not playing the deuce, it would surely be demonstrably wrong.]
The point here is that I do not believe JF's rollouts of the illustrated position can be trusted, and that it would seem reasonable to question JF's rollouts of any position in which a rolling prime is involved.
You have seen an example of what can happen if a prime that only has one pip left to be rolled forward is mishandled. Now back up the prime, and you can imagine how the error could be multiplied. By making lower board points (particularly the ace point), even when wrong, JF avoids reaching a position where it won't misplay again!
Newer versions of JellyFish continue to emerge and improve, yet still need to fully appreciate the value of a rolling prime. When JF hits a shot from a backgame, its containment policy places too great an emphasis on closing inner board points and too little on forming/strengthening a prime. This means that JF is vulnerable to a greater chance of a fluky escape, and it fails to capitalize on the optimal strategy of generating numbers that will force a second blot -- to maximize the number of such opportunities. As a consequence, JF's rollouts evaluate backgames and (to a lesser degree) deep holding games to be weaker than they are in actual play.
This defect has a retrograde effect on checker moves in earlier, undeveloped positions: JF perceives too much upside and not enough downside in making lower board points. The larger the gap between the ace point and the next point made, the more likely the potential strategical resource of a prime has been lost, and the greater the JF misevaluation could potentially be.
To summarize:
- JF's evaluation of a candidate move should be adjusted favorably towards the side who is more likely to end up with multiple checkers back as a result of vulnerability to hits or a hit exchange.
- Candidate moves which make (or even hit or slot) lower board points (particularly when higher points are gapped, and there is still the potential for that side to reach a backgame-ish position) should be evaluated lower than JF indicates. Look for these themes in the notes to the game below.
How much should one dock "safe" plays and ace-point make/hit/slot moves? One must be careful not to get carried away. JF does, after all, play most positions very well, and to reach backgames or deep holding games often requires parlays.
JF worshippers may argue that such adjustments should be relatively small (or even negligible), and in most cases they're probably right. However, at this point, I do not believe even the top JF addicts have enough experience with the creature to authoritatively determine the size of such adjustments. Required are comparison of JF rollouts with very extensive top player rollouts in a variety of positions.
In these notes, candidate moves will be written in shorthand notation, listing only the checkers' destinations. For example, when the opening move "24/18 13/11" appears next to the diagram, I refer to it as "18,11." "JellyFish" is usually abbreviated as "JF."
And now, without further ado, let the game begin.
Ron Karr (Black) vs. Richard McIntosh (White)
Score: 4 - 4
11 Point Match
![[START]](Images/b_start.gif){kind=small}
The game was recorded on tape and transcribed by Richard McIntosh.
Rollouts were made by Richard McIntosh, using JellyFish Analyzer 2.02. Rollout results show equities for the player on move. Candidate plays were better than or within 0.100 equity of the actual plays, evaluated at level 7. The following plays were judged by the annotator not to warrant separate diagrams:
- Play 12b: 8/2 0.070 weaker than 13/7
- Play 14b: 13/8 6/4 0.057 weaker than 13/6
Parameter values for rollouts on moves were:
- level 5
- 7776 games (36x216)
- horizon 7
- seed 316
Standard deviations of equity estimates were between 0.003 and 0.011.
Parameter values for rollouts on cube decisions were:
- level 5
- 23328 games (36x648)
- full game
- seed 316
- settlement limit 0.550
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