Unpredictability, per definitions of chaotic behavior Apparently I've been confused about the meaning(s) of "chaotic behavior".  I always thought it meant that infinitesimal perturbations of a system parameter would lead to large changes in the system's behavior, and thus that the behavior of the system is effectively unpredictable even though it might be deterministic.
More recently, though, I get the impression that sometimes "chaotic behavior" has a second definition in which it simply means "aperiodic behavior". This from the paper, Complexity in Linear Systems ....  Perhaps there are additional definitions of "chaotic behavior".  But: would deterministic aperiodic behavior be effectively unpredictable in the same sense as the unpredictability per the first definition?  
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But: would deterministic aperiodic behavior be effectively unpredictable in the same sense as the unpredictability per the first definition?

Not necessarily. By your definition, this includes quasiperiodic behaviour, i.e., a superposition of two (or more) periodic behaviours with incommensurable frequencies. Such a dynamics is characterised by two (or more) zero Lyapunov exponents and no positive ones. As a positive Lyapunov exponent directly indicates sensitivity to initial conditions, we do not have this problem and the ensuing issues of unpredictability. All you need to know for prediction are the phases of each of the underlying oscillations and tiny errors in the measurement of these have an equally large consequence in the error of your prediction.
As a very practical example, the moon’s position in relation to the sun and earth is quasiperiodic on historic time scales (with the incommensurable frequencies being the synodic period, nodal and apsidal precession). Yet eclipses are quite famously predictable centuries in advance.
