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Alfred J. van der Poorten

Publications and source records attributed to Alfred J. van der Poorten.

7 recordsLinked to original sources
arXiv2006

Hyperelliptic curves, continued fractions, and Somos sequences

We detail the continued fraction expansion of the square root of a monic polynomials of even degree. We note that each step of the expansion corresponds to addition of the divisor at infinity, and interpret the data yielded by the general expansion. In the quartic and sextic cases we observe explicitly that the parameters appearing in the continued fraction expansion yield integer sequences defined by bilinear relations instancing sequences of Somos type.

math.NT↗
arXiv2004

Genus 2 curves, continued fractions, and Somos sequences

We detail the continued fraction expansion of the square root of monic sextic polynomials. We note in passing that each line of the expansion corresponds to addition of the divisor at infinity, and interpret the data yielded by the general expansion. In particular we obtain an associated Somos sequence defined by a three-term recurrence relation of gap~6.

math.NT↗
arXiv2004

Recurrence Relations for Elliptic Sequences: every Somos 4 is a Somos $k$

In his `Memoir on Elliptic Divisibility Sequences', Morgan Ward's definition of the said sequences has the remarkable feature that it does not become at all clear until deep into the paper that there exist nontrivial such sequences. Even then, Ward's proof of coherence of his definition relies on displaying a sequence of values of quotients of Weierstraß$σ$-functions. We give a direct proof of coherence and show, rather more generally, that a sequence defined by a so-called Somos relation of gap 4 always also is given by a three term Somos relation of all larger gaps 5, 6, 7, $... $.

math.NT↗
arXiv2004

Elliptic curves and continued fractions

We detail the continued fraction expansion of the square root of the general monic quartic polynomial, noting that each line of the expansion corresponds to addition of the divisor at infinity. We analyse the data yielded by the general expansion. In that way we obtain `elliptic sequences' satisfying Somos relations. I mention several new results on such sequences. The paper includes a detailed `reminder exposition' on continued fractions of quadratic irrationals in function fields.

math.NT↗
arXiv2004

Pseudo-elliptic integrals, units, and torsion

We remark on pseudo-elliptic integrals and on exceptional function fields, namely function fields defined over an infinite base field but nonetheless containing non-trivial units. Our emphasis is on some elementary criteria that must be satisfied by a squarefree polynomial whose square root generates a quadratic function field with non-trivial unit. We detail the genus 1 case.

math.NT↗