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In mathematics, in the field of algebraic number theory, a modulus (plural moduli) (or cycle, or extended ideal) is a formal product of places of a global field (i.e. an algebraic number field or a global function field). It is used to encode ramification data for abelian extensions of a global field. ==Definition== Let ''K'' be a global field with ring of integers ''R''. A modulus is a formal product : where p runs over all places of ''K'', finite or infinite, the exponents ν(p) are zero except for finitely many p. If ''K'' is a number field, ν(p) = 0 or 1 for real places and ν(p) = 0 for complex places. If ''K'' is a function field, ν(p) = 0 for all infinite places. In the function field case, a modulus is the same thing as an effective divisor, and in the number field case, a modulus can be considered as special form of Arakelov divisor. The notion of congruence can be extended to the setting of moduli. If ''a'' and ''b'' are elements of ''K''×, the definition of ''a'' ≡∗''b'' (mod pν) depends on what type of prime p is: *if it is finite, then :: :where ordp is the normalized valuation associated to p; *if it is a real place (of a number field) and ν = 1, then :: :under the real embedding associated to p. *if it is any other infinite place, there is no condition. Then, given a modulus m, ''a'' ≡∗''b'' (mod m) if ''a'' ≡∗''b'' (mod pν(p)) for all p such that ν(p) > 0. 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「Modulus (algebraic number theory)」の詳細全文を読む スポンサード リンク
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