BGonline.org Forums

Late Game 65

Posted By: Daniel Murphy
Date: Thursday, 27 September 2012, at 10:09 p.m.

In Response To: Late Game 65 (niuniuch)

It's likely that 11/6 11/5 is a lot more dangerous than it seemed to you over the board, and 11/5 10/5 is a lot safer than it seemed. The main reason, probably, is that hitting an immediate shot is so gammonish that your opponent will not be able to correctly hit an immediate shot nearly as often as you may have thought.

Take 11/6 11/5. No shots now, but if I count numbers that on subsequent turns clear or almost clear the 10 point, or leave a blot, or play safely for at least one roll, and then estimate how often the position repeats over the next few rolls, I get this:

7/36 clear or almost clear, 23/36 play safely in the board, so 6/36 + (23/36 * 6/36) + (23/36 * 23/36 * 6/36) + (23/36 * 23/36 * 23/36 * 6/36) numbers leave a blot on the 10 point over your next four turns. That's about 39%, but that's way too low, since with every turn that doesn't clear you have fewer numbers that you can play safely. Let's guess that you actually have about a 45% chance of blotting while trying to clear the 10 point. If so, then you'll get hit perhaps about 22% of the time over those turns. Since your opponent's board or prime will be getting better with every turn, you'll lose a lot of those games.

The other play is 11/5 10/5, leaving two blots. This appears to leave 20/36 shots immediate shots. But, first, with best play by White it doesn't leave that many shots, because White doesn't want to gammon himself! And second, since White's position will usually be a mess when he hits, you'll have lots of return hits, and also have numbers that enter and safety your other blot. I'll try to count how you often hit back (usually winning) if you're hit after 11/5 10/5:

White's roll	Your return hits
66	1 * 2 = 2
65	2 * 14 = 28
64	2 * 13 = 26
63	none! best play is 11/5 8/5
62	none! best play is 11/5 7/5
61	2 * 12 = 24
52	none! best play is 13/11 12/7
51	none! best play is 12/7 8/7
43	none! best play is 13/10 11/7
42	none! best play is 10/6 5/3
33	1 * 14 = 14

So -- after 11/5 10/5, with best play only 8/36 numbers hit -- not 20/36, and not the 16/36 or so that would hit over your next four turns after the other play, and when you get hit, you hit back immediately hit about a third of the time.

That seems a whole lot safer. But you will often leave a shot next roll too. About half your numbers will clear or nearly clear both blots, but the other half will leave a blot. Fortunately, only 6-6 will leave a direct shot. The rest are all indirect sevens. And getting hit 1/6 of 1/2 the time is only going to add the equivalent of another 3/36 hits. So, over the next two rolls, you get hit about 11/36 of the time, and you still win over 1/3 of those sequences.

There are probably too many assumptions here for real good accuracy, but I notice that in terms of GWC only, the two plays seem pretty close. So at DMP 11/6 11/5 might even be best, since White will be much less reluctant to hit. But at the score gammons make 11/5 10/5 the stand-out play, and even better if White hits with numbers that he shouldn't hit with.

Messages In This Thread

• Late Game 65
  niuniuch -- Thursday, 27 September 2012, at 7:59 p.m.
  • Late Game 65
    Casper van der Tak -- Thursday, 27 September 2012, at 9:15 p.m.
  • Late Game 65
    Daniel Murphy -- Thursday, 27 September 2012, at 10:09 p.m.
  • Late Game 65
    niuniuch -- Friday, 28 September 2012, at 4:24 p.m.
    • Rollout at DMP
      niuniuch -- Friday, 28 September 2012, at 5:23 p.m.