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Rollout: Find a 2

Posted By: Timothy Chow
Date: Friday, 19 March 2010, at 3:27 a.m.

In Response To: Find a 2 (Timothy Chow)

OTB, I thought that I didn't want another checker sent back, so I played bar/24 13/11. However, there are a couple of things wrong with this reasoning. Part of the problem is that if I get hit on the 1-point, there's a good chance I'll get one or even two more checkers sent back anyway, so 13/11 isn't any safer. Much more importantly, though, cleaning up the blot in my home board and making a 4-point table is HUGE. I gain tremendously in the variations in which I get hit but manage to hit back.

To see that the strong board is the main reason bar/24 5/3 is right, we can examine variations of the position. Suppose we take the spare on the 5-point and use it to cover the blot on the 3-point. In this altered position, bar/24 13/11 is much better than bar/24 4/2 or bar/24 6/4. Alternatively, let's keep the blot on the 3-point but move White's blot back one pip to Blue's bar point. Now there is no duplication of 5's and bar/24 5/3 allows White to hit with any roll except 4-3, while bar/24 13/11 cuts us down to 28 shots. Nevertheless, the two plays are very close on GNU 4-ply (the rollout is still running).

gnubg	95
tchow	140
Position ID: tu0BQwB0d0BwQA Match ID: UYkIACAAEAAA

#		Ply	Move	Equity
•	1	R	bar/24 5/3	-0.950
			0.219 0.037 0.002 - 0.781 0.510 0.009 -1.042 -0.950 0.002 0.001 0.000 - 0.002 0.002 0.001 0.005 0.006
			Full cubeful rollout with var.redn.
			1296 games, Mersenne Twister dice gen. with seed 850605875 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	bar/24 13/11	-1.073 ( -0.123)
			0.190 0.037 0.001 - 0.810 0.562 0.010 -1.153 -1.073 0.001 0.001 0.000 - 0.001 0.003 0.001 0.004 0.006
			Full cubeful rollout with var.redn.
			1296 games, Mersenne Twister dice gen. with seed 850605875 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

• Find a 2
  Timothy Chow -- Thursday, 18 March 2010, at 1:49 a.m.
  • Find a 2
    Chase -- Thursday, 18 March 2010, at 2:39 a.m.
    • Correction: 5/3, not 5/2 [nt] *NM*
      Chase -- Thursday, 18 March 2010, at 8:40 a.m.
  • Find a 2
    nori -- Thursday, 18 March 2010, at 4:17 a.m.
  • Rollout: Find a 2
    Timothy Chow -- Friday, 19 March 2010, at 3:27 a.m.
    • Rollout of variant
      Timothy Chow -- Friday, 19 March 2010, at 4:11 p.m.
      • Rollout of variant
        Chase -- Friday, 19 March 2010, at 6:09 p.m.