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64P-33B-41 — 53P-33B-41 — 61P-33B-41 — 3-ply XG2 Rollouts

Posted By: Chase
Date: Tuesday, 12 March 2013, at 3:59 a.m.

In Response To: 64P-33B-41 — 53P-33B-41 — 61P-33B-41 — 3-ply XG2 Rollouts (Taper_Mike)

I suspect it's a combination of things.

Blue has more material to attack with after 61P-33B-41S than with the other plays, so it makes sense that it's more dangerous for White to break anchor with a hit.

Then, as you say, there's Blue's priming prospects. Imagine each position after Blue slots then successfully makes his 5pt. It's no coincidence that the more compact the resultant prime (in the best case, a solid 4-prime; in the worst case, not much of a prime at all) the stronger slotting looks. In the stronger priming cases, not only are there fewer gaps for Blue to fill, there are (consequently) fewer available points available for White to re-anchor as a defense against the prime. (In the case of Blue's made 2pt, even re-achoring on Blue's 1pt is usually adequate.)

Finally there is the race. The farther behind Blue is in the race, the more attractive slotting is. In the case of the made 2pt, the race is almost exactly tied after Blue plays his 41, so getting hit is more costly. It's true we're only talking about a few pips in the opening of a long game, but bots can be very sensitive to tiny racing leads, even in the very early game.

Just for kicks, I asked XGR++ how to play 41 after the following (illegal) openings. Call them 75P-33B-41 and 22D-33B-41.





White is Player 2

score: 0
pip: 155
Unlimited Game
Jacoby
pip: 155
score: 0

Blue is Player 1
XGID=-B--b-D-B---cE-b-c-e----B-:0:0:1:41:0:0:1:0:10
Blue to play 41

1.XG Roller++24/23 24/20eq: -0.406
Player:
Opponent:		40.40% (G:8.85% B:0.18%)
59.60% (G:16.06% B:0.56%)
2.XG Roller++24/20 6/5eq: -0.427 (-0.021)
Player:
Opponent:		39.66% (G:9.64% B:0.21%)
60.34% (G:17.85% B:0.83%)

eXtreme Gammon Version: 2.10
White is Player 2

score: 0
pip: 155
Unlimited Game
Jacoby
pip: 159
score: 0

Blue is Player 1
XGID=----b-E-CB--cC-b-c-e----B-:0:0:1:41:0:0:1:0:10
Blue to play 41

1.XG Roller++13/9 6/5eq: -0.174
Player:
Opponent:		46.52% (G:10.29% B:0.39%)
53.48% (G:15.43% B:0.67%)
2.XG Roller++24/23 24/20eq: -0.238 (-0.063)
Player:
Opponent:		45.04% (G:8.91% B:0.31%)
54.96% (G:15.04% B:0.49%)

eXtreme Gammon Version: 2.10

Notice that the artificial positions are pretty consistent with the observations above with respect to their effects on the number of men in the zone, priming potential, and racing prospects.

And, predictably, we see the same pattern found in the original rollouts: each time we move the newly made point backward (or forward) a point, the difference between the Slot and Up plays changes by about 0.020.

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