Man versus machine

Not surprisingly, I was playing some backgammon against the computer today. What was surprising, to me at least, was the following position came up that got marked as “doubtful” by GnuBG:


Now, I didn’t even think about this one, clearly the right move is 11/7,10/7 and making the 6 prime. But GnuBG said no, 10/6, 9/6 is better. Huh?

GnuBG says 10/6, 9/6 has equity +0.788, 11/7, 10/7 has equity +0.715; a difference of -0.073 and so a blunder! Extreme gammon rates it similarly, 10/6, 9/6 gets +0.797 while 11/7, 10/7 gets +0.736, a difference of -0.061 and again a blunder!

It gets worse for me. After the next exchange of rolls, I was at the following position:


D’uh – clearly 9/2 is the right move. But no, GnuBG says 7/2, 5/2!!! 9/2 has +0.728 equity, versus +0.792 for 7/2, 5/2, a difference of -0.064 and so another blunder! Extreme gammon agrees again.

The key here is the cube. With the cube in the middle, the moves I actually made are the correct moves. But the cube has already been offered and taken, and that makes a difference. I no longer have the option to double red out after a rough roll, I have to take what I get – and if I get something bad red has the redouble.

As it happens, what I got was a 5-6 on the first roll bearing in against the men still on my one point, forcing me to leave two blots. Red rolled a 5, putting me on the bar, I danced, and then got redoubled out. So it really could have worked out better for me. But the main thing was these back-to-back positions where the difference in correct play depends so much on the cube position.

This table shows the winning chances for each move for the first position, per GnuBG:

Win W g W bg Lose L g L bg
11/7, 10/7 0.811 0.129 0.005 0.189 0.005 0.000
10/6, 9/6 0.835 0.146 0.005 0.165 0.005 0.000

And this is the equity, depending on who owns the cube:

Equity Cube in Middle Equity, Red’s cube Equity, Black’s cube
11/7, 10/7 +1.000 +0.715 +1.000
10/6, 9/6 +0.934 +0.788 +0.978
Difference +0.066 -0.073 +0.022

Very similar charts for the second position:

Win W g W bg Lose L g L bg
9/2 0.824 0.115 0.004 0.176 0.005 0.000
7/4, 7/3 0.833 0.145 0.006 0.167 0.005 0.000
Equity Cube in Middle Equity, Red’s cube Equity, Black’s cube
9/2 +1.000 +0.728 +1.000
7/4, 7/3 +0.925 +0.781 +0.970
Difference +0.075 -0.053 +0.030

I find it also interesting that the drop in equity for leaving an indirect shot is a lot lower when black owns the cube in both positions as well. I think either of these would make a good “quiz” question for Phil Simborg. Having them back to back like that in a game definitely made me stop and think about the value of owning the cube!


June 18th Backgammon Tournament Results

We had an incredible turnout at Occidental Brewing this afternoon – 20 players! That is, in fact, a new record. There were a lot of newcomers or people returning after a long absence as well – I think 7 or 8 people I had not had the pleasure of meeting before.

We caught the management off guard – I should have scoped out the location earlier and I would have learned that they were a little on the smaller size, in the area we took over. Probably should have given them a head’s up, but Sara and others smoothed some feathers with the staff and once we got running, it went very smoothly. If we go there again, we’ll warn them, and probably move to the upstairs space, which is (I’m told) a little larger (I never made it up there today). Martin assured me that this is the best brewery in Portland, even though it is somewhat out of the way for people, based on the majority of comments I got.

Being such a large group, I divided us up into two brackets. You would think 20/2 = 10, but with the chaos of filling in the brackets as a few stragglers rolled in, we ended up with 9 in the A bracket and 11 in the B bracket. Oh well!

The “A” bracket ended up in a newcomers show-down. Karen beat out William for 1st, and Billy won the consolation bracket. The “B” bracket went to the established crew, with Nick beating out Gints for the big prize. I squeaked out a win in the consolation bracket, mainly because Mark F left “early” – I would have had to face him again, but he didn’t want to stick around another half hour or so for the $10 entry refund that went to third place. So: payday!

Greg made the suggestion that the consolation bracket should run 3 point matches instead of 5 point matches, in order to wrap up a little faster. By definition the consolation bracket starts later, and so it was running long. Thanks for the suggestion, Greg, we will definitely do that next time!

The other big thank you goes to my daughter, Kira, who took over the clipboard while I played and helped keep the tournaments running smoothly. What a great Father’s Day gift, eh?

All in all, we did manage to finish the tournament by 6, although Nick and Bryan were observed playing a money game as I headed out. Some people never get enough, I suppose. If you want more, we’ll do it again next month at Great Notion, on July 16th. I’ll call and warn them first!

Player Initial Elo Rating Matches Played Matches Won Final Elo Rating
Mark F 1542.6 4 4 1604.62
Karen 1500.0 4 4 1568.85
Nick 1500.0 3 3 1554.27
Billy 1500.0 4 3 1530.34
Bryan 1544.6 3 1 1523.25
Mark 1534.4 3 1 1518.88
WIlliam 1500.0 3 2 1517.10
Joel 1500.0 3 2 1513.56
Noah 1500.0 3 2 1513.53
Mally 1500.0 4 2 1506.43
Greg 1500.0 4 2 1500.15
Paul 1508.5 3 1 1492.50
Gints 1469.3 3 2 1491.31
Karla 1500.0 3 1 1483.08
Martin 1500.0 2 0 1468.08
Donnelle 1500.0 2 0 1466.07
Kristin 1500.0 2 0 1465.10
Julie 1502.8 3 0 1452.32
Sara 1482.1 2 0 1450.28
Justin 1480.7 2 0 1445.35

June 10, 2017 Chouette Results

We had a record turnout for the Chouette this month – 9 people! I was hoping we would break into double digits, but maybe next month. Mark F, fresh off his second place finish in the Chicago Open Master’s, was feeling peppy going in, and he was in charge of the “advanced” board. He asked me not to mention how he did, you can draw your own conclusions there. Julie took over the “beginner” board, where she held the box for a long, long time against newcomers Tanya and Ted. They had a lively time with lots of discussion about the best moves at each point. That left Gints and I on the “middle” board, which, if you count carefully, does not equal a chouette. But we had fun anyway.

Gints and I are pretty evenly matched at backgammon, and we ended up taking pictures of a LOT of positions for later analysis. The ones I took, I have to say, most of them were not that close – I was offering doubles much too early and accepting them much too late. But occasionally, they were interesting, as in the following:


Here I’m red, Gints is white, I have two on the bar and am being redoubled. Would you have offered that double? Would you take in my place?

The race is actually pretty even, he’s up 132 to 143. My risk is, nothing is especially holding him back at this point. He has 4 and 6 to hit my blot in the outfield, worst case scenario is bring the back checker around. Seems like a pass to me, and it is. In fact, it is too good to redouble! Winning chance is at 76%, but 44% is gammons. GnuBG says no double has equity +1.117, XG says +1.141. I’m about to get buried here, and I took the chance to drop. If you don’t think about the gammon chances, it seems like a close call, but the majority of the losses are gammons, and since the cube has already been turned, they count.

Anyway, a good time all around – we’ll do it again next month!


June/July 2017 Calendar

We’ve got the next few Chouettes & Tournaments on the calendar – check it out:

Chouettes will be on the second Saturday of each month through August – so June 10th, July 8th, and August 12th. They will all be at Lucky Labs on Hawthorne – that’s 915 SE Hawthorne Blvd if you want the actual address. Turnout has been pretty consistent so far, I hope we will build it up to be able to consistently have two tables going by the fall. Play starts at 1:00 and goes until 5:00 or so, depending on when people fall out.

We will have the June tournament on the 18th at Occidental Brewing, 6635 North Baltimore Avenue, starting at 1:00. Format to be determined – I’m thinking we’ll probably go back to a single double elimination bracket unless the turnout is pushing 16. Last time around, we moved it up to 5 point matches, and no-one complained, so we will likely do that again.

For July, the tournament will be on the 16th at Great Notion, 2204 NE Alberta St #101, again starting at 1:00. Same caveats as for June. Have you noticed a theme of North Portland based venues? I figure we will keep moving each month until someplace just screams to be the new “permanent” home.

See you there!