Last night an old idea came back to me, an idea about a function where all the derivatives start from zero and then grow smoothly. I thought it would be impossible, but then I found some interesting stuff on Wikipedia. So, I learned to use SymPy and wasted a lot of time with it. Here's a report of my (non-)findings.
(UPDATE: I did some numerical differentiation, which showed that h(x) does have negative derivatives. See details in this comment. A disappointment, although perhaps not a surprising one. It doesn't however, necessarily mean the goal is impossible.)
So, if anyone knows whether such a function exists and what it looks like, please tell me.
That's what I thought too, but it turns out that is not true! Here's a couple of interesting links: Non-analytic smooth function, Bump function, Flat function. EDIT: Fixed the links and added another one.
Thanks for the links. This is outside the area of math I usually deal with, but I agree it's interesting. I think I understand what you're asking for now, but I've hit my mental limit for today trying to work it out. Good luck in your search!