On computing the Lyapunov exponents of reversible cellular automata
Springer
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We consider the problem of computing the Lyapunov exponents of reversible cellular automata (CA). We show that the class of reversible CA with right Lyapunov exponent 2 cannot be separated algorithmically from the class of reversible CA whose right Lyapunov exponents are at most 2-delta for some absolute constant delta>0. Therefore there is no algorithm that, given as an input a description of an arbitrary reversible CA F and a positive rational number epsilon>0, outputs the Lyapunov exponents of F with accuracy epsilon. We also compute the average Lyapunov exponents (with respect to the uniform measure) of the reversible CA that perform multiplication by p in base pq for coprime p,q>1.