How to do this? Different Choseable Limitations which don't always Apply

[evileeyore]

I'm trying to build a power but I suspect it will be easier (but more costly?) to make it an Alternate Ability of itself.

What I want it to be able to chose from a set of Power Modifiers when the power is activated, a specific number of which must be used. For example if the build has the choices of; Costs Fatigue 1 (-5%), Side Effect (-5%), and Counter Measures (-5%); the user must chose 2 of these for the power to work.

Either it will cost 1FP and have a Side Effect or Cost 1 FP and have Counter Measures or have a Side Effect and Counter Measures.


I could swear once that I saw a way to do this, but I can't find it anymore. I do know I could just build 3 AAs, but I that ends up being more expensive than I think it's worth.

[PK]

You're probably thinking of Alternative Rituals from GURPS Thaumatology: Sorcery, which treats "choose any two of: Costs Fatigue, 1 FP (-5%), Accessibility, Requires gestures (-10%), and Accessibility, Requires magic words (-10%)" as a single -5% limitation.

I've lost since lost the notebook on which I did some crazily scribbled math, but what I came up with is that "choose any two of these three or four -10% limitations" is fairly priced at -5%. And since, deep in my heart of hearts, I consider Costs Fatigue to be more fairly priced at -10%/level, I went with that -5%.

So if you're willing to accept my word for it, I can assure you that "choose any two of these three or four -5% limitations" would be worth about -2.5%.

[Anaraxes]

There's also a method called "Either/Or" for multiplying two Limitation values together to arrive at a price for being able to choose either one of those two on the fly, each time the ability is used. It's in PU8, Limitations, or originally appeared here.

http://forums.sjgames.com/showthread.php?t=8504

[PK]

Originally Posted by Anaraxes

There's also a method called "Either/Or" for multiplying two Limitation values together to arrive at a price for being able to choose either one of those two on the fly, each time the ability is used. It's in PU8, Limitations, or originally appeared here.

http://forums.sjgames.com/showthread.php?t=8504

Right, and that was the base of the math, but it gets far more complex when you try for a "choose X of Y" where Y > X > 1.

[Kalzazz]

Using that post, choosing between two 20% limitations is 4%

Sorcery is choosing 1 of 3 20% limitations (since 2 10% limitations = 20%, and are 3 ways to pick 2 of 3)

[evileeyore]

Originally Posted by PK

...GURPS Thaumatology: Sorcery...

I haven't found time to read that yet. It's been on my to-do list... looks like it's moving up to the top of the reading list.

So if you're willing to accept my word for it, I can assure you that "choose any two of these three or four -5% limitations" would be worth about -2.5%.

That sounds much better than the alternative below...

Originally Posted by Anaraxes

There's also a method called "Either/Or" for multiplying two Limitation values together to arrive at a price for being able to choose either one of those two on the fly, each time the ability is used. It's in PU8, Limitations, or originally appeared here.

http://forums.sjgames.com/showthread.php?t=8504

Thank you, yes that's exactly what I was thinking of. For some reason yesterday I forgot PU:Limitations existed and never looked in the Power-Ups series at all.

[PK]

Originally Posted by evileeyore

That sounds much better than the alternative below...

No, it's consistent with that alternative. That's the fair value for "Choose one of these limitations." Obviously, having to choose two will be worth more.

[Kalzazz]

Choosing 1 of 2 20% limitations is 4%

Why should choosing 1 of 3 bundles of 20% (2 10% limitations) limitations be 5%?

I admit I do not follow

[Ulzgoroth]

Originally Posted by Kalzazz

Choosing 1 of 2 20% limitations is 4%

Why should choosing 1 of 3 bundles of 20% (2 10% limitations) limitations be 5%?

I admit I do not follow

The overlap between the bundles would certainly make it more of a limitation than if it was picking one of three totally independent limitations.

[Varyon]

Originally Posted by Ulzgoroth

The overlap between the bundles would certainly make it more of a limitation than if it was picking one of three totally independent limitations.

Roughly speaking, as choosing 1 of 2 equal-value Limitations ends up giving you -|limitation|^2 as the value, and choosing 1 of 3 is -|limitation|^3, it would make sense for 2 of 3 (generalized to n of m) to be -|limitation|^(3/2) (generalized to ^(m/n). For 2 of 3 -10% Limitations, that's a bit over -3%, which can be rounded up to -5% (3 of 4 is -4.6%).

From that, it might be appropriate, when dealing with n of m Limitations of unequal value, to multiply them all together, then take the nth root. So, for two -20% and a -10%, where you have to pick 2, that would be -(.2*.2*.1)^(1/2) = -6.3%.

Granted, that's not the way I'd handle it, but that's because I don't like the way Alternative Limitations are currently handled. It seems to me to be more appropriate to base how much they're modified off of how close they are in value, rather than just what their absolute numbers are - I've mentioned it before, but my preference is to have equal-value Limitations use 80% of their nominal value, unequal ones to get closer to 100% of the lower value the further apart they are (I'm currently leaning toward 80% for 1.5x or less difference, 85% for 2x, 90% for 3x, 95% for greater differences; for more than two choices, work out what it would be for combining the two most expensive, then combining the most expensive remaining with that combination, and so forth). n of m isn't something I'd considered before, so I'd have to see what I could work out for that...