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52S-xxx-42, data

Posted By: Nack Ballard
Date: Monday, 7 June 2010, at 2:35 a.m.

In Response To: 52S-63R-42? Subject changed to catch Nack's attention (Timothy Chow)


1O '1O ' '5X '3X ' ' '4O

1X ' ' ' '5O '4O '1X '5X

52S-63R-42


Thanks, Tim. I hadn't and haven't read the other posts. As you suspected, I would have bypassed this thread completely if you hadn't put an opening move string in the post header.

The Snowie truncated rollout I have for 52S-63R-42 (diagrammed above) is [@ P21], while the full rollout (though no live cube) gives [@ P6] 5k. It's too little data to make strong conclusions, but if we average the two low-quality results we get [@ P13], meaning that @ is best and P is -.013, and we might say that there is an anti-P trunc bias of .008.

Here are Snowie trunc results for all 52S-xxx-42 positions I have where @ (anchoring on the 20pt) and P (making the 4pt) are the two top plays:

52S-21S-42 [@ P66] tr
52S-41T-42 [@ P25] tr
52S-41U-42 [@ P9] tr
52S-42P-42 [@ P87] tr
52S-43S-42 [@ P66] tr
52S-51R-42 [@ P34] tr
52S-51S-42 [@ P35] tr
52S-52D-42 [@ P73] tr
52S-52S-42 [@ P35] tr
52S-54S-42 [@ P56] tr
52S-61P-42 [@ P64] tr
52S-62S-42 [@ P49] tr (hitting is a whopper)
52S-63R-42 [@ P21] tr, and [@ P6] 5k no live cube
52S-63S-42 [@ P31] tr
52S-64P-42 [P @16] tr
52S-65R-42 [@ P24] tr

If the trunc bias I inferred earlier is is our best guess, then decrease the above error sizes by 8 (thousandths) except increase that of 52S-64P-42 (from 16 to 24).

Paul and I had thought (after proper rollout verification) to make 52S-42P-42 and 52S-64P-42 a contrasting spread (as shown below) in one of our books. But really what it comes down to is that @ (anchoring on Opp's 5pt) beats P (making own 4pt) for all 52S-xxx-42 positions except when xxx is 64P (or 41U is likely a tie).


1O '1O2X '4X '2X ' ' '4O

2X ' ' ' '5O '4O ' ' '5X

52S-42P-42: anchor (generally right anyway)



1O2X1O ' '4X '2X ' ' '4O

2X ' ' ' '5O '4O ' ' '5X

52S-64P-42: make the 4pt (exceptional position)


Related situations arise with 32S-xxx-31, 32Z-xxx-31 and 52S-xxx-31 (see Backgammon Openings). In those cases you should almost always play P (make 5pt) instead of @ (anchoring on Opp's 4pt). It's the converse paradigm.

I tell my students that a good rule of thumb is:

Either 5pt beats either 4pt.

Nack

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