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Late blitz cube quiz
Posted By: Timothy Chow In Response To: Late blitz cube quiz (Timothy Chow)
Date: Monday, 31 October 2011, at 3:22 p.m.
About a year ago, I posted a quiz with eight problems. If you missed it, you may want to click here to look at the problems before reading on.
I provided rollouts but no commentary because I felt I didn't really understand the positions. With a little more experience under my belt, I offer the following tentative analyses of problems 1, 2, 3, 4, and 8. Problems 5, 6, and 7 I would now classify as containment cubes rather than blitz cubes and fall into a separate category. I may comment on them at some later time, but not today.
First, a general comment. I believe that when deciding whether to take a late blitz cube like this, it is very important to try to forecast how the game is going to play out, and in particular how you think you can win the game. For early blitzes, remembering a few reference positions and observing a few static features (race, number of checkers in the zone, number of points in each home board, etc.) is often enough to get you in the right ballpark. Late blitzes are much more diverse and I don't think that approach works unless you have a much larger database of reference positions under your belt.
To get a sense for how the game will play out, Stick recommends playing it out interactively. This may work for him and for others, but I've never been a fan of it because there's too much luck involved with the dice. It's like doing a rollout without variance reduction. Instead, I've found GNU's temperature map feature more useful. Your mileage may vary.
Now for the positions.
1. This one is close to being an opening blitz, so static evaluation is not such a bad approach. On the downside, White's four-point board is a serious threat. Also, White has nineteen rolls that hit a second blot. On the other hand, White currently has only eight checkers in the zone, and has two checkers still on her 24pt. Blue has some good defensive structure established: his 4pt and 11pt. How is Blue going to win this game? White misses half the time, and Blue is a favorite to come in. White can keep trying to hit loose, but Blue's return hits are quite potent. It's not that easy for White to keep the attack going and close Blue out if she gets a third checker sent back. If Blue anchors he's right back in the game.
2. Things look pretty bleak for Blue at first glance. White has almost escaped and has many rolls that make a five-prime. She has her best three-point board and many checkers in the zone. However, it's important to note that although White has many threats—safetying the back checker, making a five-prime, making a fourth point in her board—she can't do them all at once. For example, if White rolls 41, does she make her bar point or does she safety her blots with 18/13? Similarly, what does she do with a 65? If she doesn't safety her blot on the 18pt, Blue has quite a few return shots which will equalize the game or even turn it around because of his strong board and the close race. If Blue simply enters, which he is a favorite to do, and slips by White's blockade, his racing chances will be reasonable. Finally, let's note that Blue's gammon losses should be relatively low here; much of White's equity comes from priming rather than attacking. This is a take, but note that it's quite sensitive to seemingly small changes in the position, such as the position of White's rearmost checker. Move that checker from White's 18pt to her 16pt and it's probably a drop. Blue will have fewer return shots and his strong board will be correspondingly less useful.
3. I think this is the position that is hardest to evaluate. XG seems to be a bit more sanguine about Blue's chances, judging it to be close to a take if not an actual take. It's hard to evaluate because there will quite likely be a blot-hitting contest and it's hard to estimate Blue's chances of coming out on top when the dust settles. White will hit loose with any 5 or 1, as well as with 44 or 62. If Blue hits back, he has a three-point board to greet White, and his 7pt and 8pt also block White to some degree. However, White is anchored and has a four-point board. This is a good position for experimenting with variants to get a sense for how much various features of the position matter. As a practical matter, if you're the stronger player, I think this is a good practical take, because the ensuing game is complex with many opportunities for mistakes. Some players may not hit loose as White, or even if they know to hit loose immediately, they may not know what to do with weaker rolls (bring more checkers down to attack? start to escape the back checkers?). The game could turn around quickly and if you send the cube back, they may make a mistake with the take/pass decision.
4. The one response I got to this quiz, by someone called David, remarked that he thought that the position in Problem 4 was worse for Blue than in Problem 3, because Blue has no board here. It's instructive to compare the two positions. I'd say that the first big point in Blue's favor is that White has only a three-point board here rather than a four-point board. That's big, even though White has a dilly builder in Problem 3. White will still hit loose, but it's easier for Blue to survive. White will have no trouble re-entering after getting hit, of course, but her checkers will still have to navigate through the obstacle course in Blue's outfield to return to the scene of action. Blue's broken outfield prime may not seem like much, but it still poses problems for White since she already has three checkers way back and might get some more sent back in the upcoming melee. For example, if we pull up Blue's 11pt and put a spare on each of his 8pt and 10pt, then this gives Blue 4 extra pips in the race but weakens his blockade, and the take becomes more questionable.
8. When I first encountered this position, I thought that White still had a lot of work to do to get her checkers around, and that if I hit a checker, I'd be right back in the game with my four-point board. So I took. This was a serious mistake. White's position is very strong here, and she probably would have at least an initial double even if Blue were already anchored on the 24pt! How come? It's true that White won't have an easy time coming around the board without leaving shots, but even if she is hit, Blue is far from home free. Blue has a four-point board, it is true, but he has a gap on his 4pt, and more importantly, too much of his army is too far away from the front lines. White will typically re-enter and just try again, and Blue will still have to escape two checkers from behind White's four-prime. He will have trouble sustaining an attack. White isn't the only one who might leave blots, and if Blue gets hit again at some point, he will be in big trouble. Not only is there serious gammon danger with White's strong board and race lead, Blue's winning chances are lower than in your average blitz. This is a big pass.
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