The aim of this note is to mention some potential tools for studies of chaotical behaviour of rays. First a local exponential divergence of rays in a phase-space is demonstrated. Next the possibilities of a study of ray chaos by means of the Lyapunov exponents for both continuos time-evolution and iterative maps on Poincare sections are discussed. In the continuos case the Lyapunov exponents can be obtained from the analyses of the propagator matrices and in the latter problems their discrete analogies have to be constructed. The correlation technique is then shortly pointed out and the employment of wavelet multiresolution analysis is proposed in the last part of the note.
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