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In [[mathematics]], '''Eisenstein's theorem''', named after the German mathematician [[Gotthold Eisenstein]], applies to the coefficients of any [[power series]] which is an [[algebraic function]] with [[rational number]] coefficients. Through the theorem, it is readily demonstrable that a function such as the [[exponential function]] must be a [[transcendental function]]. | |||
Suppose therefore that | |||
:<math>\sum_{}^{} a_n t^n</math> | |||
is a [[formal power series]] with rational coefficients ''a''<sub>''n''</sub>, which has a non-zero [[radius of convergence]] in the [[complex plane]], and within it represents an [[analytic function]] that is in fact an algebraic function. Let ''d''<sub>''n''</sub> denote the [[denominator]] of ''a''<sub>''n''</sub>, as a fraction [[in lowest terms]]. Then Eisenstein's theorem states that there is a finite set ''S'' of [[prime number]]s ''p'', such that every prime factor of a number ''d''<sub>''n''</sub> is contained in ''S''. | |||
This has an interpretation in terms of [[p-adic number]]s: with an appropriate extension of the idea, the ''p''-adic radius of convergence of the series is at least 1, for [[almost all]] ''p'' (i.e. the primes outside the finite set ''S''). In fact that statement is a little weaker, in that it disregards any initial [[partial sum]] of the series, in a way that may ''vary'' according to ''p''. For the other primes the radius is non-zero. | |||
Eisenstein's original paper is the short communication | |||
''Über eine allgemeine Eigenschaft der Reihen-Entwicklungen aller algebraischen Functionen'' | |||
(1852), reproduced in Mathematische Gesammelte Werke, Band II, Chelsea Publishing Co., New York, 1975, | |||
p. 765–767. | |||
More recently, many authors have investigated precise and effective bounds quantifying the above [[almost all]]. | |||
See, e.g., Sections 11.4 and 11.55 of the book by E. Bombieri & W. Gubler. | |||
==References== | |||
*{{Cite book|last = Bombieri|first = Enrico|authorlink=Enrico Bombieri|coauthors = [[Walter Gubler|Gubler, Walter]]|section=A local Eisenstein theorem|section=Power series, norms, and the local Eisenstein theorem|title=Heights in Diophantine Geometry|publisher=Cambridge University Press|year=2008|pages=362–376|doi= 10.2277/0521846153}} | |||
{{DEFAULTSORT:Eisenstein's Theorem}} | |||
[[Category:Theorems in number theory]] | |||
Revision as of 13:50, 11 December 2013
In mathematics, Eisenstein's theorem, named after the German mathematician Gotthold Eisenstein, applies to the coefficients of any power series which is an algebraic function with rational number coefficients. Through the theorem, it is readily demonstrable that a function such as the exponential function must be a transcendental function.
Suppose therefore that
is a formal power series with rational coefficients an, which has a non-zero radius of convergence in the complex plane, and within it represents an analytic function that is in fact an algebraic function. Let dn denote the denominator of an, as a fraction in lowest terms. Then Eisenstein's theorem states that there is a finite set S of prime numbers p, such that every prime factor of a number dn is contained in S.
This has an interpretation in terms of p-adic numbers: with an appropriate extension of the idea, the p-adic radius of convergence of the series is at least 1, for almost all p (i.e. the primes outside the finite set S). In fact that statement is a little weaker, in that it disregards any initial partial sum of the series, in a way that may vary according to p. For the other primes the radius is non-zero.
Eisenstein's original paper is the short communication Über eine allgemeine Eigenschaft der Reihen-Entwicklungen aller algebraischen Functionen (1852), reproduced in Mathematische Gesammelte Werke, Band II, Chelsea Publishing Co., New York, 1975, p. 765–767.
More recently, many authors have investigated precise and effective bounds quantifying the above almost all. See, e.g., Sections 11.4 and 11.55 of the book by E. Bombieri & W. Gubler.
References
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