Problem 64 From 501 (Part 1)

This is the first problem I am going to tackle out of 501, and part of my goal in doing so is to attempt to delve into a more detailed analysis of a position to see how much I can learn. The position may be getting more analysis then it deserves, but it is the learning process that I am interested here more so than the position itself. I have picked this position because it is the first one I encountered (skipping chapter 1) where the answer in the book seems to be incorrect.

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Red to play 14

 

Pip counts: Blue 121, Red 83
Position ID: m22BgEG2cxsEAA Match ID: QYkQAAAAAAAA

After making a fairly quick first pass through 501 I am now working through the positions in much more detail. I was proud of myself when I came up with the same play as Robertie for this position, that play is 13/12* 7/3.

My reasoning for this play was that it maximizes builders for the ace point. This is the same reasoning that Robertie gives, noting that making the ace point will increase the gammon chances.

So far so good, unit I start analyzing the position in GNUBG and then what do I find?

#		Ply	Move	Equity
	1	R	13/12* 8/4	+1.238
			0.908 0.458 0.007 – 0.092 0.003 0.000 +1.278 +1.238 0.001 0.001 0.000 – 0.001 0.000 0.000 0.002 0.003
			Full cubeful rollout with var.redn.
			2592 games, Mersenne Twister dice gen. with seed 870065397 and quasi-random dice
			Play: world class 2-ply cubeful prune [world class]
			keep the first 0 0-ply moves and up to 8 more moves within equity 0.16
			Skip pruning for 1-ply moves.
			Cube: 2-ply cubeful prune [world class]
•	2	R	13/12* 7/3	+1.228 ( -0.010)
			0.902 0.464 0.007 – 0.098 0.004 0.000 +1.271 +1.228 0.001 0.001 0.000 – 0.001 0.000 0.000 0.002 0.003
			Full cubeful rollout with var.redn.
			2592 games, Mersenne Twister dice gen. with seed 870065397 and quasi-random dice
			Play: world class 2-ply cubeful prune [world class]
			keep the first 0 0-ply moves and up to 8 more moves within equity 0.16
			Skip pruning for 1-ply moves.
			Cube: 2-ply cubeful prune [world class]

Close, but 13/12* 8/4 is just a bit better, the extra gammons from 13/12* 7/3 don’t quite make up for the extra losses, but what is going here? Why is the 7/3 worse?  Answering these questions is where the real learning lies, and that is the subject of Part 2.

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