|
In number theory, an algebraic integer is a complex number that is a root of some monic polynomial (a polynomial whose leading coefficient is 1) with coefficients in (the set of integers). The set of all algebraic integers is closed under addition and multiplication and therefore is a subring of complex numbers denoted by A. The ring A is the integral closure of regular integers in complex numbers. The ring of integers of a number field ''K'', denoted by ''OK'', is the intersection of ''K'' and A: it can also be characterised as the maximal order of the field ''K''. Each algebraic integer belongs to the ring of integers of some number field. A number ''x'' is an algebraic integer if and only if the ring () is finitely generated as an abelian group, which is to say, as a . ==Definitions== The following are equivalent definitions of an algebraic integer. Let ''K'' be a number field (i.e., a finite extension of , the set of rational numbers), in other words, for some algebraic number by the primitive element theorem. * is an algebraic integer if there exists a monic polynomial such that . * is an algebraic integer if the minimal monic polynomial of over is in . * is an algebraic integer if is a finitely generated -module. * is an algebraic integer if there exists a finitely generated -submodule such that . Algebraic integers are a special case of integral elements of a ring extension. In particular, an algebraic integer is an integral element of a finite extension . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「algebraic integer」の詳細全文を読む スポンサード リンク
|