[dietrichepp]

Do you mean "smooth everywhere"? The Weierstrauss function is continuous everywhere, but you wouldn't use it for interpolation:

http://en.wikipedia.org/wiki/Weierstrass_function

[ycombobreaker]

Yes, thank you. After reading a bit more, smoothness is what I'm looking for. One of the _derivatives_ of the smoothstep is discontinuous at the endpoint.