An attractor which "… describes motion made up of two independent oscillations" (J. CRUTCHFIELD et al., 1989, p.42)
Such a motion is "sometimes called quasi-periodic"(lbid)
J. CRUTCHFIELD et al. point out that :" The important feature of quasi-periodic motion is that in spite of its complexity it is predictable. Even though the orbit may never exactly repeat, if the frequencies that make up the motion have no common divisor, the motion remains regular. Orbits that start on the torus near one another remain near one another, and long term predictability is guaranteed." (Ibid).
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