Backgammon strategy

[magnum108]

5 point match. Result: 0-0. Yellow on the BAR.
Yellows turn. Cube or no? If yellow doubles - does purple take or pass?

[euklid314]

I guess double-take.

The only part I am very sure is, that I would take as blue since it is prime vs. prime and blue has good counterchances - even if yellow gets his 6-prime.

[Waikirikiri]

As Blue I would probably decline the double.

Yellow has 5/6 of a prime, Blue has 4/6.

Blue is less likely to escape the Yellow partial prime - Yellow has a greater chance of escaping the Blue partial prime.

If I was feeling adventurous I would accept as Blue and double back.

[Doc Odd]

In this scenario, Blue has multiple disadvantages and should not accept a double.
1. Yellow can escape more easily than Blue.
2. Blue is vulnerable to 1-6, 6-1, 2-5, 5-2, 3-4, and 4-3.
3. If Yellow does NOT get back on the board quickly, and/or Blue fails to escape the Yellow home area quickly, then Blue must continue advancing the rest of their pieces and their whole defense collapses while they are still trapped.

On the flip side, Yellow should not double, because they have enough advantage that they might be giving up a Gammon.

[euklid314]

I just entered the position in XG (=Extreme Gammon) and know the answer now. 2-ply and rollout give the same answer.

I will not (yet) reveal the solution because others might want to analyze this interesting position. Thank you, magnum108.

At the moment of my post we have the following guesses:
euklid314: Double - Take
Waikirikiri: Double - Pass (or as blue being adventurous: Double-Redouble)
Doc Odd: Too good to double - Pass

[monthemeeple]

Is this not the backgammon match play game, rather than just the plain bg game? (Although imo they should just do away with the plain one, make the match play default seeing as you can disable the cube, and it's a MUCH better interface)

[JonnyBlazin5]

It looks like a double-pass to me.

Yellow has significant threat to hit the chequer on the 7 point and send 3 back.

Also, if Yellow does not double and misses the chequer, there is a good chance that blue will cover and then the game is much more even. So now is the time to double.

I look forward to hearing what XG says!

[euklid314]

Warning: Spoilers ahead! If you want to think about magnum108´s posting yourself do not look at my text and my pictures. These contain the solution according to a rollout of XG.

I entered the position and that is what you get. If you are not familiar with XG analysis I will delve into that below.

https://imgur.com/a/VTzBdOV

First of all it is Double/Take.
But it is only a borderline double. Not doubling is only a -0,019 mistake, which is below the commonly used error-threshold of -0,020.
It would be a horrible blunder to pass. One would lose -0,467 equity by passing, which is six times the commonly used blunder threshold of -0,080.

At the moment yellow has only a winning chance of 63,54%, i.e. blue wins in 36,46% of all games. Also, the gammon chances are not that bad with yellow winning 20,81% gammons but blue also winning 12,93% gammons.

The rule that I have learned, namely "never" to pass a prime vs. prime position turned out to be correct in this position. Yellow has many rolls after which blue wants to play on - especially with the cube in his hand:
6-6,6-5,6-4,5-5,5-4,4-4 ... XG evaluates the position as even
5-1,3-3 ... blue has still a good game
5-3,4-1,2-1,3-1,1-1 ... blue is in a tough spot but can still fight
all the other rolls are market losers for yellow, i.e. if he doubles after these good rolls blue will pass. Exactly because of these market losers yellow should double now. The volatility is high at the moment (+0,207)!

https://imgur.com/a/mkihBSu

Even if you put yellows checker from the bar onto his 24-point it is still a clear take for blue (a double blunder to pass). Only if you put the yellow checker from the bar onto his 23-point you have to pass as blue - since every 5 and 6 will hit and destroy your prime.

P.S.: How could magnum108s insert a picture in his post? I tried the img and /img tags (in brackets) but it did not work...