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Advanced Backgammon part 25A ROLLOUT

Posted By: Matt Cohn-Geier
Date: Friday, 10 July 2009, at 2:14 a.m.

In Response To: Advanced Backgammon part 25A (Matt Cohn-Geier)

Position 241:

Robertie claims that for long-term safety with no other considerations, 5/4 5/3 is best. I'm not sure if this is true or not, but the timing considerations make 4/3 2/off a next here since White will break his board if he doesn't throw a 6.

Move number 7: Blue to play 21

White	110
Blue	54
Position ID: u20BADi+vQ0AAA Match ID: QQkFAAAAAAAA

• Blue moves 4/3 2/off

#		Ply	Move	Equity
•	1	2	4/3 2/off	+1.1546
			0.9006 0.3684 0.0188 - 0.0994 0.0000 0.0000
	2	2	4/3 4/2	+1.0432 ( -0.1114)
			0.8822 0.3099 0.0096 - 0.1178 0.0007 0.0000
	3	2	5/4 5/3	+1.0061 ( -0.1485)
			0.8816 0.2745 0.0089 - 0.1184 0.0003 0.0000
	4	2	6/5 6/4	+1.0039 ( -0.1507)
			0.8735 0.2886 0.0114 - 0.1265 0.0000 0.0000

Position 242:

According to Robertie, the usual strategy is to hit, forcing White to enter behind and guaranteeing only a single shot. This being the exception, staying even which may save a roll, and not having to worry about future jeopardy since White will have to break his board to stick around.

In any case, taking two off is nextish here.

Move number 9: Blue to play 32

White	72
Blue	18
Position ID: 29sGACB+AwAAAA Match ID: QYkJAAAAAAAA

• Blue moves 3/off 2/off

#		Ply	Move	Equity
•	1	R	3/off 2/off	+0.8745
			0.8771 0.1640 0.0013 - 0.1229 0.0000 0.0000 +0.9195 +0.8745 0.0010 0.0004 0.0001 - 0.0010 0.0000 0.0000 0.0021 0.0025
			Full cubeful rollout with var.redn.
			1296 games, Mersenne Twister dice gen. with seed 863379768 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	3/1* 3/off	+0.7117 ( -0.1628)
			0.8456 0.0791 0.0002 - 0.1544 0.0000 0.0000 +0.7706 +0.7117 0.0005 0.0002 0.0001 - 0.0005 0.0000 0.0000 0.0011 0.0014
			Full cubeful rollout with var.redn.
			1296 games, Mersenne Twister dice gen. with seed 863379768 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]

Position 242 (Variant):

This came up in a local chou. I argued that taking two off was right, because I believed something that wasn't in Robertie: it's virtually always right to rip checkers. As it turns out the hit is correct here. What's different?

Well, this is almost the worst case scenario for Blue, since White will stick around for a coup unless Blue rolls a 1. In addition he has tremendous timing, enough to easily pick up two checkers. It'd possibly be different if White had a closed board and two checkers on the 18 point--there's little gammon consideration but also little chance of picking up a second blot.

Interestingly the hit wins more games & gammons but not as many BGs. Various rollouts with cube access show it as a slight error to marginally correct, depending on score, position & value of the cube. Holding the cube for money, the hit is about .03 better than ripping.

Move number 5: Blue to play 62

White	141
Blue	16
Position ID: 2LaJSCC+AQAAAA Match ID: QQkLAAAAAAAA

• Blue moves 3/1* 3/off

#		Ply	Move	Equity
•	1	R	3/1* 3/off	+1.2582
			0.8260 0.6919 0.0034 - 0.1740 0.0000 0.0000 +1.3473 +1.2582 0.0013 0.0007 0.0003 - 0.0013 0.0000 0.0000 0.0028 0.0052
			Full cubeful rollout with var.redn.
			1296 games, rollout as initial position, Mersenne Twister dice generator with seed 863546533
			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	3/off 2/off	+1.1648 ( -0.0934)
			0.8076 0.5498 0.0953 - 0.1924 0.0000 0.0000 +1.2604 +1.1648 0.0026 0.0018 0.0011 - 0.0026 0.0000 0.0000 0.0056 0.0075
			Full cubeful rollout with var.redn.
			1296 games, rollout as initial position, Mersenne Twister dice generator with seed 863546533
			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]

Messages In This Thread

• Advanced Backgammon part 25A
  Matt Cohn-Geier -- Monday, 6 July 2009, at 7:11 a.m.
  • Robertie's picks
    Matt Cohn-Geier -- Monday, 6 July 2009, at 6:31 p.m.
  • Advanced Backgammon part 25A
    neilkaz -- Monday, 6 July 2009, at 8:36 p.m.
  • Advanced Backgammon part 25A
    Chuck Bower -- Monday, 6 July 2009, at 9:37 p.m.
  • Advanced Backgammon part 25A
    Seth -- Thursday, 9 July 2009, at 10:52 p.m.
  • Advanced Backgammon part 25A ROLLOUT
    Matt Cohn-Geier -- Friday, 10 July 2009, at 2:14 a.m.
    • 242-V @DMP
      Chuck Bower -- Friday, 10 July 2009, at 1:52 p.m.