I'm trying to create a parametric retractable fabric shading family. The part I'm getting hung up on--the first part--is how to make a parametric parabola (or reasonable-looking approximation). Imagine holding a piece of fabric along two opposite edges... it droops down in the center in the shape of a parabola. Move the edges closer together and you it droops lower, pull them apart and it flattens out. How would you go about making this? Can I do it as a regular family? Does it need to be an adaptive component? What do you think?