Position #27

[PersianLord]

Position information:

Pip-count: Red 109-107 White
Score:       Red     0-0     White
Match:                   7-pointer

White on roll. Proper cube action?

Spoiler

I will provide the analysis and rollouts after I get a decent evaluation here. 

[close]

[PersianLord]

5 votes till now and no analysis 

[playBunny]

Lol, I'll bite - even though I got it wrong.

Spoiler

I voted double/pass. I counted the number of closes, hits, safe moves and dodgy moves for white and reckoned that there were good gammon chances, though not enough for Too good to double. I was tempted to say take because the race is so close and there are holes in the rolls where white can't make hay and red gets a chance to run but I was a tad too wary of the gammons and plumped for the drop.

GnuBg 2-ply said it was a blunder to drop (-.100), 4-ply agreed but thought it not so terrrible (-.77). 3-ply said it was a doubtful drop (-.37). The 2-ply rollout is still going but so far it agrees with 3-ply (adding fuel to the debate about which of 2-ply and 3-ply is to be trusted). Given the expected Doubtful verdict I won't hang my head in shame for dropping.

[close]

[PersianLord]

Lol, I'll bite - even though I got it wrong.

Spoiler

I voted double/pass. I counted the number of closes, hits, safe moves and dodgy moves for white and reckoned that there were good gammon chances, though not enough for Too good to double. I was tempted to say take because the race is so close and there are holes in the rolls where white can't make hay and red gets a chance to run but I was a tad too wary of the gammons and plumped for the drop.

GnuBg 2-ply said it was a blunder to drop (-.100), 4-ply agreed but thought it not so terrrible (-.77). 3-ply said it was a doubtful drop (-.37). The 2-ply rollout is still going but so far it agrees with 3-ply (adding fuel to the debate about which of 2-ply and 3-ply is to be trusted). Given the expected Doubtful verdict I won't hang my head in shame for dropping.

[close]

Spoiler

Thank you for the analysis.

Exactly that was my verdict as well (D/P) and here what I wrote in my blog last night:

During my actuall match against GNUBG, I dropped the cube and was sure that my decision should be right. Why?

i) There are 16 rolls for white which enables him to point on red's blot : 6/1-6/3-6/4 , 4/1-4/3, 3/1 and four doublets : 1/1-2/2-3/3-4/4. In other words, white is ~44% likely to point on red's blot which will be very painful for red.

ii) Even if white is unable to point on red's blot, there will be very few rolls that might be bad for white, mainly 6-6. (~3%) and even after white's immediate miss, red will face extreme difficulties in escaping from the white's 4-prime

iii) White is ahead in the race now by 2 pips and after rolling, this gap will widen almost surely.

So, all in all, there is little hope for a winning strategy for red and it seems that passing is very clear. Yet, GNUBG favores the take:

2-ply cubeless equity  +0.526 (Money:  +0.523)

   73.2%   9.0%   0.2% -  26.8%   3.1%   0.1%

Cubeful equities:

1. Double, take         +0.908
2. Double, pass         +1.000  ( +0.092)
3. No double            +0.711  ( -0.197)

Proper cube action: Double, take

As you see, GNUBG considers passing as an almost blunder (-0.092). Why?

[close]

[playBunny]

Cube Rollout

Spoiler

2-ply rollout shows that it's not such a blunder to have dropped. I had leaned towards the take because of the close race and the White rolls that don't close Red out. Red escapes completely with 6-6, 6-5, 6-4, 6-2, 5-5 and 5-3, and two of those give a racing advantage. Red can also take chances with 6-1, 5-2 and 5-1 and go for the 50-50 race if missed. Some of White's rolls that point on Red will leave a couple of shots off the bar. A 6-6 for White would even leave a direct shot. Against Red's formidable home table a hit would be a big swing of fortune, gammon chances for Red. My decision fell on the cautious side but GnuBg sees enough in all that to make the take worthwhile, though it's not a grab-the-cube-before-they-change-their-mind kind of take.

Cubeless equity  +0.526 (Money:  +0.523)

Cubeful equities:
1. Double, take         +0.960
2. Double, pass        +1.000  (+0.040)
3. No double            +0.735  (-0.225)

Proper cube action: Double, take

The blah blah ...

Full cubeful rollout with var.redn.
1296 games, Mersenne Twister dice gen. with seed 822800576 and quasi-random dice
Play: supremo 2-ply cubeful prune [world class]
keep the first 0 0-ply moves and up to 16 more moves within equity 0.32
Skip pruning for 1-ply moves.
Cube: 2-ply cubeful prune [world class]
Different evaluations after 12 plies:
Play: 0-ply cubeful prune [expert]
Cube: 0-ply cubeful prune [expert]

[close]

[PersianLord]

Cube Rollout

Spoiler

2-ply rollout shows that it's not such a blunder to have dropped. I had leaned towards the take because of the close race and the White rolls that don't close Red out. Red escapes completely with 6-6, 6-5, 6-4, 6-2, 5-5 and 5-3, and two of those give a racing advantage. Red can also take chances with 6-1, 5-2 and 5-1 and go for the 50-50 race if missed. Some of White's rolls that point on Red will leave a couple of shots off the bar. A 6-6 for White would even leave a direct shot. Against Red's formidable home table a hit would be a big swing of fortune, gammon chances for Red. My decision fell on the cautious side but GnuBg sees enough in all that to make the take worthwhile, though it's not a grab-the-cube-before-they-change-their-mind kind of take.

Cubeless equity  +0.526 (Money:  +0.523)

Cubeful equities:
1. Double, take         +0.960
2. Double, pass        +1.000  (+0.040)
3. No double            +0.735  (-0.225)

Proper cube action: Double, take

The blah blah ...

Full cubeful rollout with var.redn.
1296 games, Mersenne Twister dice gen. with seed 822800576 and quasi-random dice
Play: supremo 2-ply cubeful prune [world class]
keep the first 0 0-ply moves and up to 16 more moves within equity 0.32
Skip pruning for 1-ply moves.
Cube: 2-ply cubeful prune [world class]
Different evaluations after 12 plies:
Play: 0-ply cubeful prune [expert]
Cube: 0-ply cubeful prune [expert]

[close]

Thank you for rollout and analysis.

But PB, I still favor the drop. Why? Well, backgammon is a game of probablities and we can't rely on desired "lucky" rolls to change the discourse of a game. In this position, 44% of the times, white will point on red, which may even lead to gammons (9%). In other 54%, most of them white will widen the gap in race. From the rolls you pointed to, in 6-1, 5-2 and 5-1, white still will be the CLEAR favorite, and in other cases, just in 5-5 and 6-6 red will probably become the slight favorite. but they're just 6% likely to happen, right?

well, all in all, I will pass this everytime I'm offered, but I admit that my skills certainly don't match yours and GNUBG's. lol

[blitzxz]

I'm very doubtful about gnu's evaluation here. It doesn't make sense to go for take where risk for losing is huge and even 4 points is not that far away. 4-0 would be big lead in 7-point match and 1-0 wouldn't mean almost nothing. There's also possibilities for red to win 4 points with redouble if he escapes. Holding cube with even race is clear advantage but that's still far from this position. Practically it's okei to take if you are underdog. That will shorten the match and maximaze luck. But if you're favorite to win, take is very bad. Even the gnu's "objective" judgement might change if you make longer rollout. (I started to make 2-ply rollout with just little bit better settings then playBunny and after 200 games it's still showing pass. 3-ply might be interesting but that takes a week or so..)

[socksey]

This is the beginning of a 7 pt match.  So, what if there is a gammon?  Great chance of white to hit and cover.  If not, red still has a chance to save that beautiful board and hit later.  Be brave!  Double take!   

socksey



"If you don't read the newspaper you are uninformed; if you do read the newspaper you are misinformed. - Mark Twain

[PersianLord]

I agree wholeheartedly with blitzxz  . If your rollout shows that D/P is instead correct, then my initial analysis will get credit, lol. I'm awaiting to see your ultimate analysis/rollout.

Regards

[blitzxz]

I agree wholeheartedly with blitzxz  . If your rollout shows that D/P is instead correct, then my initial analysis will get credit, lol. I'm awaiting to see your ultimate analysis/rollout.

Regards

I made the rollout and it was even closer but still take. 3-ply might chance things...  Any way pass and take are so close here that practical reasons are more important.

Cube analysis
Rollout cubeless equity  +0,538 (Money:  +0,536)

Cubeful equities:
1. Double, take         +0,977
2. Double, pass         +1,000  ( +0,023)
3. No double            +0,741  ( -0,236)
Proper cube action: Double, take
Rollout details:
Centered 1-cube:
  0,739 0,081 0,001 - 0,261 0,023 0,001 CL  +0,538 CF  +0,741
[0,001 0,001 0,000 - 0,001 0,001 0,000 CL   0,002 CF   0,004]
Player You owns 2-cube:
  0,750 0,079 0,001 - 0,250 0,022 0,001 CL  +1,140 CF  +0,977
[0,001 0,002 0,000 - 0,001 0,001 0,000 CL   0,005 CF   0,006]
Full cubeful rollout with var.redn.
1296 games, Mersenne Twister dice gen. with seed 822562662 and quasi-random dice
Play:  2-ply cubeful prune [world class]
keep the first 0 0-ply moves and up to 8 more moves within equity 0,12
Skip pruning for 1-ply moves.
Cube: 2-ply cubeful prune [world class]

[PersianLord]

This is the beginning of a 7 pt match.  So, what if there is a gammon? 

lol, then can't I ask that "so, what if you lose the match right away?" 

[socksey]

   It's happened!  

The point is, it was FUN!  

socksey



"I don't make jokes; I just watch the governmentand report the facts." - Will Rogers