I'm testing a surface mesh generator that takes a function $f:\mathbb{R}^3 \rightarrow \mathbb{R}$ and builds the surface described implicitly by $f(x,y,z)=0$. I already tested with a torus, a ball and an ellipse and things work perfectly well.
I'd like to come up with a "fancier" surface now, something which is not "standard" but that vary in space smoothly, but I can't think of any equation for this one. Does anybody has a good candidate?