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Rollout: The perils of reference positions

Posted By: Timothy Chow
Date: Saturday, 3 July 2010, at 3:18 a.m.

In Response To: The perils of reference positions (Timothy Chow)

The position that I had seen before was position 101 of 501 from Robertie's book. In that position, 13/8 13/7 clearly tops the rollout, and 24/13 is a quintuple whopper! So in the position at hand, I figured that breaking anchor couldn't be right. It's true that the two positions aren't quite the same, but could the differences really be significant enough to turn running from a 0.513 error into the right play?

Apparently so. See the rollout below. Running does get gammoned significantly more often, but the extra wins are apparently more than enough to compensate. In Robertie's position, Blue has a decent chance of building a winning prime if missed. In my position, White has a slightly better anchor and I am too far advanced. Even if I am not hit, it is very hard for me to make and hold a good prime. Most likely I will crunch or be forced to run anyway at an even less favorable moment. The best chance is to run now. However, it still surprises me that the extra gammon losses are an acceptable price to pay. Note that the difference in cubeless equity is not so large, so perhaps part of the story is that Blue gets more use out of the cube in the positions that result when Blue runs.

Any further insights would be appreciated.

gnubg	120
tchow	139
Position ID: tm2CARjMnoUBMA Match ID: cAkaAAAAAAAA

#		Ply	Move	Equity
•	1	R	24/14	-0.839
			0.360 0.107 0.007 - 0.640 0.376 0.019 -0.561 -0.839 0.002 0.001 0.000 - 0.002 0.002 0.001 0.004 0.013
			Full cubeful rollout with var.redn.
			1296 games, Mersenne Twister dice gen. with seed 892606473 and quasi-random dice
			Play: supremo 2-ply cubeful prune [world class]
			keep the first 0 0-ply moves and up to 16 more moves within equity 0.32
			Skip pruning for 1-ply moves.
			Cube: 2-ply cubeful prune [world class]
	2	R	13/9 13/7	-0.934 ( -0.095)
			0.302 0.070 0.004 - 0.698 0.243 0.019 -0.585 -0.934 0.002 0.001 0.000 - 0.002 0.002 0.001 0.004 0.013
			Full cubeful rollout with var.redn.
			1296 games, Mersenne Twister dice gen. with seed 892606473 and quasi-random dice
			Play: supremo 2-ply cubeful prune [world class]
			keep the first 0 0-ply moves and up to 16 more moves within equity 0.32
			Skip pruning for 1-ply moves.
			Cube: 2-ply cubeful prune [world class]

Messages In This Thread

• The perils of reference positions
  Timothy Chow -- Friday, 2 July 2010, at 2:05 a.m.
  • The perils of reference positions
    Bob Koca -- Friday, 2 July 2010, at 3:53 a.m.
  • The perils of reference positions
    Chuck Bower -- Friday, 2 July 2010, at 6:06 p.m.
    • The perils of reference positions
      Timothy Chow -- Friday, 2 July 2010, at 6:20 p.m.
  • Rollout: The perils of reference positions
    Timothy Chow -- Saturday, 3 July 2010, at 3:18 a.m.
    • Rollout: The perils of reference positions
      Bob Koca -- Saturday, 3 July 2010, at 10:41 a.m.
      • Rollout: The perils of reference positions
        Timothy Chow -- Saturday, 3 July 2010, at 10:30 p.m.