Sensitivity to initial conditions and Lyapunov exponent of a quasiperiodicsystem

The dynamics of a quasiperiodic map is analyzed both in the presence and in the absence of weak noise. It is shown that, in the presence of weak noise , a strange chaotic attractor with a negative Lyapunov exponent and sensiti ve dependence of trajectories on the initial conditions can exist in the sy stem. This means that the types of motion of a fluctuating system cannot be classified only by the sign of the leading Lyapunov exponent. (C) 2000 MAI K "Nauka/Interperiodica".