Well all physical systems are actually nonlinear; linearity is something we use when we can. I would call those types of nonlinear control toy problems compare

Well all physical systems are actually nonlinear; linearity is something we use when we can. I would call those types of nonlinear control toy problems compared with nonlinear systems like the climate or society. But agree that we just don't know the equations or the variables. I still would argue that at least with many nonlinear systems, they are intrinsically unpredictable the farther into the future you go because of their sensitivity to initial conditions, self-organization and nonlinear internal dynamics. I'm referring to the statistical long tail: http://en.wikipedia.org/wiki/Long_Tail http://en.wikipedia.org/wiki/Long_Tail For more details: http://tuvalu.santafe.edu/~aaronc/courses/7000/csci7000-001_2011_L2.pdf http://tuvalu.santafe.edu/~aaronc/courses/7000/csci7000-001_...