Backgammon Strategy--Backgames

Strategy--Backgames

Which anchors are best?

From:   Chuck Bower
Address:   bower@bigbang.astro.indiana.edu
Date:   21 January 1997
Subject:   Re: How bad is this hit?
Forum:   rec.games.backgammon
Google:   5c34a9$4rk@dismay.ucs.indiana.edu

Dan Scoones wrote: > Last night on FIBS I played my first-ever match with TD_one. After > splitting my back men and getting pounded by a quick 55, I managed to > struggle my way to this 2-5 backgame: > > +-24-23-22-21-20-19-+---+-18-17-16-15-14-13-+ > | O X O O X O | | O | > | O X O O X O | | O | > | O O X O | | O | > | | | | > | | | | > | | | | > | | | | [1] > | | | | > | | | | > | | | | > | X | | | > | X X X | | X | > | X X X X | | X O | > +--1--2--3--4--5--6-+---+--7--8--9-10-11-12-+ > > 1-point match > O: TD_one > X: rook > X to play 65 > > (snip) > > I played 20/9..., and managed to cover my 5-point just before TD_one > was forced to break into a double shot. I hit the shot and went on to > win a close race. I realize that Kit answered this question already, but here are some "quantitative" results. I ran JF level-6 cubeless (money play) rollouts and it gave the following results: play X's % winning chances (std. dev.) money cubeless equity 20/9 33.6(1.4) -0.548(0.038) 20/15,8/2 29.3(1.8) -0.730(0.050) 20/14,8/3 27.9(1.3) -0.729(0.034) 23/12* 28.5(1.6) -0.850(0.048) Thus JF agrees with your play, both for money and at DMP. (Note that JF is really playing with gammons ("money play") so the percentage wins will probably be differenent at DMP. Still, we can probably accept the RELATIVE values (winning chances) of these plays. > (snip) > > ...what is the probability that a properly-timed > 2-5 backgame will yield a direct shot? I've heard pretty convincing > evidence that it's one of the weakest two-point backgames of all. I can't answer this question, but I find your last comment surprising. Robertie's "Advanced Backgammon" doesn't agree with this "2-5... is one of the weakest two-point backgames of all." (WARNING: I am speaking from memory, since I don't have his book in front of me.) BTW, here I am assuming that by "two-point backgames" you mean "games where backgamer has exactly two of his/her opponent's inner board points". One way to divide these up is to look at the number of points between the two you actually hold: No points between: 12, 23, 34, 45 One point between: 13, 24, 35 Two points between: 14, 25 Three points between: 15 (I realize that backgames with the opponent's 6-point do occur, but they are so rare that I don't feel the least bit confident to even comment.) My distorted view of recent backgammon history (1970 to present) recalls that originally the 12 and 13 were the backgames that were talked about. Players quickly found that the 12 is EXTREMELY difficult to time. Then the 13 and 23 were considered the best. As time progressed, there arose a feeling (maybe just mine; history has a way of getting fuzzy) that IN GENERAL the value of a two-point backgame decreased with the number of points between. (NOTE that I said "IN GENERAL".) In "Advanced Backgammon", I seem to recall that Robertie calls the 2-5 backgame quite playable, which surprised me when I first read it. Since then my limited experience with the 2-5 has been positive (probably not "positive equity", unfortunately). As far as I know, no one has performed a systematic study of the relative merits of the different backgames using the new robots. Does anyone out there want to take on this task?? You may go down in history as the first person to really understand the relative strengths and weaknesses of the different two-point backgames! (Or maybe not...) Chuck bower@bigbang.astro.indiana.edu c_ray on FIBS

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