On 𝑃-orderings, rings of integer-valued polynomials, and ultrametric analysis
Journal of the American Mathematical Society, Tome 22 (2009) no. 4, pp. 963-993

Voir la notice de l'article provenant de la source American Mathematical Society

We introduce two new notions of “$P$-ordering” and use them to define a three-parameter generalization of the usual factorial function. We then apply these notions of $P$-orderings and factorials to some classical problems in two distinct areas, namely: 1) the study of integer-valued polynomials and 2) $P$-adic analysis. Specifically, we first use these notions of $P$-orderings and factorials to construct explicit Pólya-style regular bases for two natural families of rings of integer-valued polynomials defined on an arbitrary subset of a Dedekind domain. Second, we classify “smooth” functions on an arbitrary compact subset $S$ of a local field, by constructing explicit interpolation series (i.e., orthonormal bases) for the Banach space of functions on $S$ satisfying any desired conditions of continuous differentiability or local analyticity. Our constructions thus extend Mahler’s Theorem (classifying the functions that are continuous on $\mathbb {Z}_p$) to a very general setting. In particular, our constructions prove that, for any $\epsilon >0$, the functions in any of the above Banach spaces can be $\epsilon$-approximated by polynomials (with respect to their respective Banach norms). Thus we obtain the non-Archimedean analogues of the classical polynomial approximation theorems in real and complex analysis proven by Weierstrass, de la Vallée-Poussin, and Bernstein. Our proofs are effective.
DOI : 10.1090/S0894-0347-09-00638-9

Bhargava, Manjul 1

1 Department of Mathematics, Princeton University, Princeton, New Jersey 08544
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Bhargava, Manjul. On 𝑃-orderings, rings of integer-valued polynomials, and ultrametric analysis. Journal of the American Mathematical Society, Tome 22 (2009) no. 4, pp. 963-993. doi: 10.1090/S0894-0347-09-00638-9

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