I'm 4-0 up in a race to 7 against Gnub. Gnub doubles early on in the 5th game, but I quickly turn it around and am about to re-double after I make a very strong roll. However, if Gnub takes it is obvious it is immediately going to ship the cube straight back and we play one game for the whole match (albeit one where I have a solid edge). Gnub marks my re-double as a huge mistake with this scoreline, despite it being fine in cash play.

Does this mean that I have to drastically tighten up my doubling standard here and basically play for the Crawford game (and the subsequent games if Gnub wins the Crawford) or should I still just try and get the match ended here? It seems the numerous shots at the win I have by refusing the double (and giving gnub the chance to win the match in one game) is better equity than just putting it all up in the air in one game - am I missing something here? Should I re-double or not?

You are right. From gnus point of view it has the choice of dropping and being down 6-0 or taking the cube and playing this game for the match.

In gnu you can choose Analyze, Match equity table and you can see that gnus chances of winning the match from 1-away 7-away is roughly 9%, so if it can win this game more than 9% of the time in this game it should take and redouble for the match.

Also your doubling window here is very narrow, so you should be very close to gnus take point for the correct cube action to be double/take.

One last point if you have gammon chances then you are pretty much always either too good to double or not good enough in this situation.

Right that makes perfect sense. Ty for the very clear response and the extra points about my doubling window and gammon chances - all very interesting.

The one I've had come up a couple of times is up 4-0 with the cube, and I roll into a bearoff position that's effectively 6 checkers on the 1-point for each of us. The proper cube action there actually is redouble-take and play for the match.

I'm pretty sure you're wrong about this. I wouldn't even redouble 4 vs. 4 (which is 86-14)

I'm not sure if this is right. You lose when he hits a double in the next two rolls, but you don't:

You-Him-You-Him: Miss-Hit-Miss-Whatever --> 25*11*25*36 = 247500
You-Him-You-Him: Miss-Miss-Miss-Hit --> 25*25*25*11 = 171875

(247500+171875)/36^4 = 25%

So if you double, you're playing for the 75% equity of winning this game, which is playing for the match.

But if you just play it out, you'll be up 5-0 75% of the time with 85% equity and up 4-1 25% of the time with 71% equity. This amounts to

.75*.85 + .25*.71 = 81.5% equity.

So doubling there loses 6.5% equity.

http://gammonline.com/demo/equity.htm

(Note: I didn't factor into account doubling on the next roll. This *might* swing it, but I'm doubtful.)

Doubles is 6 outs instead of 11, but you're right anyway. How is gnu on 2-ply cube screwing that up? It's a pretty big mistake. It's also a small (1% MWC) mistake to double with 4v4, but again gnu on 2-ply cube screws it up- it drops when it should take. WTF?

I take it that this also means that if trailing 4-0 in this spot you can double much more liberally, as cube ownership is much less of an issue?

Ugh. I had "direct shots" in my head for some reason.

Can you reproduce it with a screen shot?

On a rollout, it gets it correct instantly.

It's worth pointing out that my analysis had a second error, in that I did not compute a RE-double, but rather just a straight double.

On the bottom right corner in the analysis window, it says 0-ply.

Might as well fix the analysis...

You-Him-You-Him: Miss-Hit-Miss-Whatever --> 30*6*30*36 = 194400
You-Him-You-Him: Miss-Miss-Miss-Hit --> 30*30*30*6 = 162000

(194400+162000)/36^4 = 21.2%

So if you double, you're playing for the 78.8% equity of winning this game, which is playing for the match.

But if you just play it out, you'll be up 6-0 78.8% of the time with 91% equity and up 4-2 22.2% of the time with 66% equity. This amounts to

.788*.91 + .222*.66 = 86.36% equity.

Wait.. it says cubeless 0-ply, but then it's talking about cubeful action, and you can see the settings I have. Analysis settings are the same. Is there a third place I need to change this?

What version of GNU are you using? I recently downloaded the most recent one, and I can't even find the "Evaluation Settings" window. All my settings (as best as I can tell) are under Settings -> Analysis.

Version GNU Backgammon 0.90-mingw 20090914

The most recent is 20100816, so I don't really know where your settings are located. Maybe it's time to upgrade?

Yeah, seems like it for sure. It has separate evaluation, analysis, and rollout settings. Evaluation and analysis were 3/2 forever, and rollout is variable, but obviously those aren't rollout results because it would say rollout (and because it gets it right in a rollout).