Playing on GridGammon has seen me moving from cash play to match play, with disastrous effects on my already poor cube play. In the game below, I am 4-nil down in a match to 7, and elected not to double on this and the following few throws, all of which are bad blunders. Looking at my equity, I am only 58% to win, and even less in some of the other turns that followed, yet still it is a blunder not to double. Any pointers as to what changes so I can begin wrapping my head around this?

I think we need a diagram here!

I'd probably be better off without one in most cases!

Do you understand match equities? Basically if red drops, the score is 5 away/3 away and red has 66% equity. If he takes and wins, he wins the match. 100% match equity. If he takes and loses a single point, the score is 3 away/3 away with 50% equity.

Excluding gammons to start, (there is probably a touch over 10% gammon chance here for white) red is risking 16% to win 34% equity. So he is risking 16 to win 34. The raw equity needed is 32% for a take.

You said you have about 58% winning chances. Once you turn the cube, gammons have no value for your opponent. Gammons have full value for you, since a gammon for you wins the whole match. So he has about 42% equity in wins, but since gammons are full value, each one is the value of a full game. If you win just a little more than 10% gammons, likely here, then his accumulated equity is below 32%.

Finally, he has no recube value. Once you double and he accepts it is a dead cube.

I hadn't realised match equity played such a big factor.

My thinking centred around the fact that had I cubed here, he has a match winning cube, and I would only be playing to level the score. Shouldn't that make me more hesitant to offer the cube, considering that I'm only 58% to the good? Well, that's what I'm thinking in retrospect - during the game it just looked like a complete no-double to me.

Clearly additional reading is required. Thanks for the input.

Inspired by this, I looked up Kit's match equity table and started playing around with it. It looks like OP has about 24% match equity if he doesn't double (coincidently [or maybe not...] the pre-game match equity). jjpregler has shown that take/drop is a close decision for the opponent, so equity after offering the double will be about 34% either way. Certainly, a clear double.

Generally, in contact positions, where gammon chances are present, a leader should protect his lead by doubling less aggressively, and taking more conservatively. The trailer should do the oppossite - double earlier and take later. The higher the cube level, the bigger this effect is. Non-contact positions are a different animal.

Exact match equity calculations can be complicated, but the general picture for contact positions is more or less this:

Scale for cube action:
(1) A clear favourite, but a clear money no double yet.
(2) A double/take.
(3) A double/pass.
(4) Too good to double (and a pass).

If you are way behind in a match (i.e. 0-4/7 or 0-6/11), then jump one step higher on the scale, so a close no double for money becomes double/take, or a double/take for money becomes a double/pass. If the cube is already on 2, jump 2 steps instead, so a close no double for money becomes a double/pass.

If you are the leader, jump down the scale instead, so i.e. don't double if your double would be an easy take for money.

This is way too general to use as a rule of thumb of course, but might be a starting point for getting some grip of the match cube play.

Cube actions for races are very similar to money game at most scores (unless you are doubling when 2-away, so you draw an instant recube), but on redoubles, the match equity calculations will be probably necessary.

General rules of thumb are my best friend at this point, thanks Karol.

For anyone coming across this down the line, this seems to be quite useful as well: http://www.extremegammon.com/phil1.aspx

Now it's a question of reading and understanding, and then watching it all collapse over the board. My cube play is sitting at around 21, which is costing me dearly. The main issues seem to be where I come across a situation that I've misunderstood, and so for several throws in a row I'll make the wrong call, resulting in horrific cube scores. Complicating matters with match equity just adds to the fun!

Okay, so continuing on, this situation came up:



We are both 3 away, so I get that our match equity at this point is 50/50. I've brought up the XG cube analysis window, and it seems to indicate that in this situation the "too good to double" option for red kicks in at 91%, yet this seems to contradict the analysis panel, which shows red's winning chances as 69%, yet it still suggests the situation is too good to double.

I think I am completely misunderstanding something here, any help appreciated!

You didn't mention Red's gammon chances, which plays an enormous role in these situations.

Red's (cubeless) winning chances are 69%, but his gammon chances are 45%, so it's a huge pass for money and the only question becomes "Should Red play on for the gammon?"

As always in match play, every decision has to be evaluated relative to the match score.

If Red cashes the game, he takes a 1-0 lead in a 3-point match. That's not a very big deal, since it makes him just a tad less that 60% to win the match. Winning a gammon without doubling makes him 2-0 to 3, where he's a 75% favorite. Cashing now really throws away some potential equity from his gammons, while playing on keeps the gammon alive and puts that potential equity to work.

Thanks Bill. Keeping all this in mind otb is proving to be quite tough!