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arXiv · 0910.4409

Linear Fractional Recurrences: Periodicities and Integrability

Eric Bedford·Kyounghee Kim
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Abstract

We consider k-step recurrences of the form $z_{n+k} = A(z)/B(z)$, where A and B are linear functions of $z_n, z_{n+1}, ..., z_{n+k-1}$, which we call k-step linear fractional recurrences. The first Theorem in this paper shows that for each k there are k-step linear fractional recurrences which are periodic of period 4k. Among this class of recurrences, there is also the so-called Lyness process, which has the form $A(z)/B(z) = (a +z_{n+1} + z_{n+2} + ... + z_{n+k-1})/z_n$. The second Theorem shows that the Lyness process has quadratic degree growth. The Lyness process is integrable, and we discuss its known integrals.

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Eric Bedford, Kyounghee Kim. 2009-10-22. Linear Fractional Recurrences: Periodicities and Integrability. https://arxiv.org/abs/0910.4409

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