Continuous Collatz Conjecture Has anyone studied the real function 
$$ f(x) = \frac{ 2 + 7x - ( 2 + 5x )\cos{\pi x}}{4}$$ (and $f(f(x))$ and $f(f(f(x)))$ and so 
on) with respect to the Collatz conjecture? 
It does what Collatz does on integers, and is defined smoothly on all 
the reals. 
I looked at $$\frac{ \overbrace{ f(f(\cdots(f(x)))) }^{\text{$n$ times}} }{x}$$ briefly, and it appears to have bounds independent of $n$. 
Of course, the function is very wiggly, so Mathematica's graph is 
probably not $100\%$ accurate. 

Yes, it has been studied in

Xing-yuan Wang and Xue-jing Yu (2007), Visualizing generalized 3x+1 function dynamics
  based on fractal, Applied Mathematics and Computation 188 (2007), no. 1, 234–243.
  (MR2327110).

I have found this reference in Jeffrey Lagarias's "The $3x + 1$ Problem: An Annotated Bibliography, II (2000-2009)".
This real/complex interpolation of yours is not the only one imaginable, you will find several others either in Lagarias' article cited above, or in the first part of this series of articles, namely in "The $3x+1$ problem: An annotated bibliography (1963--1999)".
