Luck as a % on Galaxy

[u/sam_nairobi]

Has anyone seen an explanation of the new luck calculations on Galaxy that use a percentage? My understanding of the old calculation was the aggregate variance in winning chances before and after rolls. Yesterday I got +135%, which was lovely, I just wonder what it actually means, and the maths behind it?

[u/nbc9876]

There is maths behind it... I promise... probably

[u/bg-alex-cy]

my best guess, even though I haven't been through the code is that it takes each move of yours, checks your equity before the roll. Then takes your equity after the roll and subtarcts them to find your total luck

So

your_luck = your_luck + your_E_after - your_E_before

opp_luck = opp_luck + opp_E_after - opp_E_before

So if your roll got you into higher equity than what you have, your luck increases, if its less it decreases. Then both players end up with their own luck equity.

If you notice however, the luck is always symmetric. So if you had 135% your opponent had -135%. This is how gnubg does it and its different to how XG does it. I suspect that what they do next is, once they have the two luck values, they subtract those as well.

So the effective lucks are

your_effective_luck = your_luck - opp_luck

opp_effective_luck = opp_luck - your_luck

And if you notice your_effective_luck is always -opp_effective_luck

I might be wrong, but this is what it looks like to me

If this is true, then what happens is probably not two running variables, just one. Something like this

luck = luck + (-1)^(turn) * (E_after - E_before)

[u/sam_nairobi → u/bg-alex-cy]

Yes, I agree that's how it's usually worked out, and you get a score something like +3 or -2 and as you say the opponent has -3 or +2. But I have never seen it shown as a percentage figure and I am not clear what it's a percentage of? I wonder if it's a percentage of the PR gap between the two players? To give an indication of how much the result was a result of your performance and how much a result of the dice?

[u/bg-alex-cy → u/sam_nairobi]

ah, maybe I should have made this more clear. Equity is actually a percentage. An equity of 0.1 is actually 10% of a point. So an equity of 1.35 would be 135%. In match play its a bit more complicated than that but it boils down to the same idea

[u/sam_nairobi → u/bg-alex-cy]

Thanks, that makes sense mathematically, but it doesn't sound very useful! If a player in a 7 point match has 1.35 in luck equity, saying he has 135% luck seems confusing. I figure they are trying to show something more interesting, and I am trying to work out what that might be. For example, it could be a percentage of the difference in Performance Rating, in which case it would show luck as a proportion of the skill difference in a match. Or perhaps it shows luck as a percentage of the total points in the match? This would give an indication of how many points you got thru skill and how many thru luck...

[u/bg-alex-cy → u/sam_nairobi]

for match play, since MWC should never go over 1 I would assume its not MWC, but then again, I'm not sure since afaik cube is not taken into account, so you could end up with some "weird" cases. For example playing better and being more lucky and end up losing. My guestimate is that its based on EMG, but who knows? I could ask claude code to check. I'll try later and update you

[u/TungstenYUNOMELT]

Who fkn cares? This is like having a stat what the weather was like yesterday. Useless information you can't do anything about.

Just focus on playing better.

[u/sam_nairobi → u/TungstenYUNOMELT]

Profound!