a graph but has forgotten the equation which goes with it.

Oh.

it's like a sine or cosine but one of the humps/troughs is fatter than the other direction. I don't particularly care which way up or where the zero line goes, though my recollection is that it all sits just above the zero and there's a relevant bit of physics with it.

this is the opposite way round to forget things because the other way around can be looked up (or calculated)!

normally losing worms rather than equations.

Yeah. Figuring out a graph from a formula, or a description is relatively easy to find out. From the graph without a good idea what you're looking at, it can be difficult to figure out.

the fat hump might be 3 times the thin trough (which just kisses the zero) but, even if I'm remembering it right, that's still not enough to go on.

Difference in heights?

was judging them as equal, ie from a central line (without that actually being a zero line).

also remembering another graph where it only has its extra wide hump as it crosses the y-axis and all the other undulations are the same width as each other (because of weird things which happen with the limits of the equation). But that's not the thingummy I want.

perhaps something like [((sin x) + 1)/2]^2

or root 2 (power 0.5) to tip it up the other way.

not be able to remember whether there was some rectified circuit involved but there might have been a scenario with a cycloid of some sort.

now that I'm looking in that direction, the specific subset I want of all the things with the various hypo / hyper / epi names is probably a curtate trochoid.

if sinc(x) is one of them = sin x / x

Sinc Function -- from Wolfram MathWorld

yes, I've definitely encountered that one.