A Relationship Between Parametric Resonance and Chaos
  In this paper we study two types of exponential instability -- parametric resonance and chaos. We show that a given equation may produce chaos or parametric resonance, depending how the problem is defined. In so doing we establish a relationship between the Floquet indices (associated with parametric resonance) and Lyapunov exponents (associated with chaos). 
R. Kobes and S. Peles