So we get some very interesting positions these days on our forum. Just wanted to share this cube decision with you.



Uploaded with ImageShack.us

Black on roll if that is not clear from the picture.

This is between Hall Skåra and Bob Wachtel from a match on TMG.

I would say with four checkers behind a four prime, a three point board and a close race that it looks like no double/take. Once red manages to anchor, the game will be very close. This might even be a beaver for money.

I pass. Black has a lot of initiative and will probably pick up the checker on the midpoint and have complete outfield control.

At the score both take point and gammon value is higher than for money, so that also push in direction of a pass, but I think this is a pass for money as well.

I cannot imagine this being even close to a pass.

Already the same split reactions like we got in our norwegian community. I like it. For me this is a double for sure. Maybe its even too good to double. For me this is a huge pass. There are so many gammons here that we lose the match too often to take this IMO. Unsure what this is for money. A beaver is beyond me. I would raccoon this in a heartbeat.

Im not very exerienced in these short match situations so I might be off in that respect. For money however, I would prop this as a big take at least for sure. Black only has 52 33 44 55 as pointing numbers (granted 66 just insta gammons), and im not sure that picking up the checker on reds midpoint with an ace changes the equity very much.

This is a little bit Escher. A static view will overestimate reds position. If we look in a dynamic way: Red is out of play for minimum two moves to do something constructive. He cannot expand his front position. If his one and only man in the outfield disappears, his army is devided. By now black has only a 3 point block, but can expand easily at both ends. If black can expand to a five prime, reds front position soon will crack. It looks now not so bad, but if you develop a vision from what might be possible, i would throw this away in a shot. Even for money this highly volatile position is not a bargain to take and can easily end up in a slaughtery. Double/drop/raccoon. Anchor punch.
At home i will set up XG and then post the RO.

Let OP do this when and if he wants. I'm sure most here has some kind of bot available and can look it up if they wish.

By the way, your educated guess about the position, please. A riddle without solution will be half the fun. It is like bgonline: after one or two days, there will be the RO. Not everything is here the problem of the week. Perhaps you should start a thread about this, RO yes or not. But it is like the potw: you can always go in grunch modus. And then, it would be nice, when the work is done and you can look instantly, if you were right. Just my opinion.

yeah sure, rollout after a couple of days is fine. I wanna see the results as well. This isn't a high traffic sub-forum, though, so just give people a little time.

grunch.

double/take

these mega backgame problems are making my head hurt, but ill give it a shot.
11-66, 51, 52, 31, 21 are all monsters for black. I am in your camp here.

too good to double / pass.

(though with the extreme confusion inherent in the position, it seems like a good practical double)

When you post the rollout, put it in spoiler tag. This way, everyone is happy.

I am a non math. This is a serious flaw in my performance, espacially in match. Often i decide by experience and “gut-feeling”. So a closer view, which is possible without bots (Stick or Bill will do this over the board, we fishes can do only an educated guess).

Five point match 3away, 3away

“Play is close to normal backgammon at this score, but you should tend to drop quicker than usual. A look at the numbers illustrates why. Let's assume gammons aren't an issue, and you are being doubled.
If you pass: You are behind 3-2, 40% equity.
If you take and win: You are ahead 4-2 (Crawford), 75% equity.
If you take and lose: You are behind 4-2, 25% equity.
As can be seen the taker is risking 15% to gain 35%. This is worse than the normal money 3 to 1 odds -- you need 30% winning chances to justify the take. If there were anything special about the recube value it wouldn't be so bad, but the recube is normal. If your opponent passes, he will be behind 4-2 (Crawford) for 25% equity. If he takes, it is for the match. Therefore your opponent will have the normal 3 to 1 odds on his take; his only disadvantage will be that the cube will now be dead so he will have to play the game to conclusion.
Since the drops come quicker at this score, the doubles come quicker also since the doubler doesn't want to lose his market. Otherwise, play is fairly normal.”
(http://www.bkgm.com/articles/GOL/Aug99/fivept.htm)

“Gammon price

The relative value of winning a gammon compared with the value of winning a single game. Gammon price is computed as GP = (WG - W) / (W - L), where WG = value of winning a gammon, W = value of winning a single game, and L = value of losing a single game. In money play, the gammon price is 50%. In match play, the gammon price depends on the score of the match and the level of the doubling cube. See posts by David Montgomery and Ron Karr." And don't forget different gammon rates. See below.

(http://www.bkgm.com/gloss/lookup.cgi?gammon+price)

So this are two major adjustments. The takepoint may be higher, and the gammon price may be higher then in cash game. If you know this, then your “gut” will tell you, that as this score, with higher gammon rates, the doubling window will significantly change. Also, the point of first and last give will be lower. It is fine, when we know it exactly, but it is better then nothing if we know this approximately.

I will show, to get a real feeling, the exact numbers(Kazaross/Rockwell MET). Non gammon adjusted, for both players:

Take point dead/alive 30,29% / 22,76%
Double Point dead/alive 50,00% / 50,00%
Cash Point dead/alive 69,71% / 77,24%
Too Good Point: dead/alive 100% /100%

Gammon adjusted, this changes dramatically (Gammon Price: 0,769).

I take the exact GR and BGR from the RO ( Skara 45,99% / 7,84%; Wachtel 31,67% / 4,88%).

Market Windows:

Take point: dead/alive; Skara/Wachtel 33,43% / 30,78%; 39,34% / 33,78%
Double Point: dead/alive; Skara/Wachtel 48,70% / 48,70%; 51,30% / 51,30%
Cash Point: dead/alive; Skara/Wachtel 60,66% / 66,22%; 66,57% / 69,22%
Too Good Point: dead/alive; Skara/Wachtel 78,36% /84,42%; 84,42% / 78,36%

So the point of first give is for Scara below even! And he can double in only up to 66,22%. Regarding 66 55 11 52 65 61 51 64 as market losers, we have a whopping 13 throws, or 36,1%, to lose our market in next turn. And if Wilcox Snellings comes the way, putting out his wallet to give one point for the cube, i would even for money decline his offer.

Because of the confidence interval, i have to crank up the rollout assuming cash game. If there is interest, i will post XG results, 3ply/3ply variance reduction, 1296 trials for match, ???? for cash game.

"Gammon adjusted, this changes dramatically (Gammon Price: 0,769)."

So you think this number, 0,768, is relevant for the original problem ?

Thanks, higonefive, for your careful analysis. Nice job.

Perhaps a little bit to much numbers. The gammonprice for cash games is always the same, 0,5. Depending on the given score, we have 0,769. Surely this is relevant. A gammonish position with different gammon rates will favour the player with the chance of higher gammon rates, because he will be paid much better(thinking in match equity). Or in another way: trailer in a postcrawford game for example has no costs for a gammon, because he loses the match anyway, he can even chose a play witch will crank up the gammons for his opponent, but give overall more won games, as the extra gammons costs nothing. The doubling windows are changing also, as you can see.
When i post the RO's for match and for cash games, you will see, that checkerplay according to the score is also affected, because we have significant different gammon rates. I have to crank the cash game RO up to 10000k, to make the take decision waterproof. So results in approximately 8 hours from now.

Let me give you a hint: The gammon value that is interesting for this position is not 0,769.

Bots are nice, but blindly copying their info without thinking is of no use.

This fish is hooked. I will prop this as a pass for money.

I think this is a pretty good take on the situation.

At first I thought this was at least a take and honestly it wouldn't occur to me to cube over the board. The more I look at it though, the more I think I agree with this analysis.

Yes, maybe it is indeed a drop but it is not easy for an amateur like me to see several moves ahead and envision the spot red will be in at that point a lot of the time.

Fascinating position, TY very much for posting. It is positions like these that give one an appreciation for just how complex and beautiful a game BG is!

If you don't think 0,769 is right, and XG delivers in the cube information wrong numbers, you are invited to explain my fault. Phil Simbourg gave on his homepage a table, titled "Rockwell Kazaross Takepoints and POG"(Price of Gammons). There we have for a centered cube 0,75. Or do you think, we have to take the gammon price for a 2-cube. 0,5?
By the way, if you look at my botless and not theoretical guess, i am not way off.
Neil Kazaross works with XG. And he was and is in the training and constructing process involved. That is for me enough reputation.
So, if there is a major flaw, please explain. But not such a girlie hint.

That was decided earlier. In a former quote you can read: "And if Wilcox Snellings comes the way, putting out his wallet to give one point for the cube, i would even for money decline his offer." But you are right, this are the positions to lure someone into a prop.

you are invited to explain my fault

And you are invited to either start thinking or staying in the aquarium.

Dude, this is a forum to learn and argue, not a bashing session. Please keep your ego at home.

Im the fish? you are the one just swimming along with the rest of the school on this problem. Just because I like to think for myself a little, and once in a while come up with a response that isn't what the popular opinion is, doesnt make me fishy. I just cant get my head around the amount of people thinking this is some monster pass for money. There is no 'being lured' here.