Please excuse the amateurish use of the term "class", I don't know what the exact term is for what I'm looking for.
Anyway, details.
I'm asking specifically about real-valued functions on the real domain ($\mathbb{R}\to\mathbb{R}$). To keep things simple, let's assume that the function is defined on some interval of interest, and is continuous and strictly monotonic in that interval, so that there is an inverse function that's also continuous and monotonic.
I am looking for a "class" of functions where the inverse is of the same "class". By "class", I mean a set of functions with a finite number parameters that, if you changed them, the function would still be in the same "class". (An obvious example of what I mean by a "class" is the polynomials: you can change the coefficients but the function is still a polynomial.) Again I apologize if this is omitting a detail or if there's a nice little word for this that I don't know.
I know of a few examples of "classes" that meet these criteria, including:
- Linear functions
- Piecewise linear functions
Polynomials, of course, do not fit this criteria in general: the inverse of a polynomial is generally not a polynomial. I don't think rational functions do either, but I'm not sure.
For the record, I am asking partly out of curiosity, and partly because I have a nice application in mind. I have a application where I need a function that can approximate a curve with perfect round-tripping ($f(f'(x))=x$, exactly). We're using piecewise linear approximation for now, but it's desirable to be smooth as well.
Thanks.