The hyperbolic paraboloid z=x^2-y^2, where we limit the surface to lie inside the cylinder x^2+y^2=1. (My previous hyperbolic paraboloid http://www.thingiverse.com/thing:934534 was limited to lie inside a rectangular region.)
One model has the equation, the other does not.
Printed one in clear and one in grey resin. Both worked well, though needed a bit of smoothing to remove the small bumps at the ends of the supports. (Not sure why some of the edges have small bumps out of them, think it is an artifact of the printing/cleaning process.)
Created the surface in Mathematica, exported the file as a .wrl to Cinema4D. Once there, I extruded the surface, then had to spend a significant amount of time repairing the mesh. I used the Optimize function, and also went around the surface repairing the mesh by hand. The equations were built in Cinema4D, then extruded. I then removed them from the surface using the Boole tool in Cinema4D.