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xxP-xxx-65

Posted By: Nack Ballard
Date: Wednesday, 16 June 2010, at 8:09 p.m.

In Response To: Another Rollout (Stick)

Here are all the rollout results I have (I think) for xxP-xxx-65 positions:

31P-32Z-65 [S R27] 5k
31P-41S-65 [S R21] 7k
31P-53P-65 [S R5] 7k
31P-55P-65 [D S39 R40] 5k 2kR
31P-63R-65 [S R25] 5k
31P-65R-65 [S R26] 7k
42P-32Z-65 [S R29] 5k
42P-21S-65 [S R5.3] 17k (GnuBG, just posted)
42P-64P-65 [R S8] 1t
53P-43Z-65 [R S35] 1t
61P-63R-65 [R P40 S63] 1t

The first seven rollouts are with Snowie, full, but no live cube. The last three rollouts are 1296-trial truncated ("1t"). Of these, Neil, 31P-53P-65, 42P-21S-65 and 42P-64P-65 look like the best candidates for XG 4-ply ROs.

Key: P = Point, R = Run, S = Split with larger number and come down with other, Z = reverse split (split with smaller number...). Error sizes are in thousandths.

After the brackets is the number of trials in thousands, rounded down ("k" is for full rollouts, "t" is for truncated). For example, "[S R21] 7k" means that S is best and R is -.021 after 7000+ trials.

In Backgammon Openings, the last paragraph on the first page of Chapter 1 states:

"Opening 31's sole weakness is that it strips the 8pt. A spare on the 8pt is so useful that Black should frequently forgo making the 5pt with 53 or running with 65 next roll. After stripping his 8pt to make his 5pt, as shown in A1, Black will often play 53 or 65 by reinforcing his underrated 8pt and splitting with the 3 or 5."

The same can be said, though to a lesser degree, about opening 42.

Nack

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