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In mathematics, a Witt vector is an infinite sequence of elements of a commutative ring. Ernst Witt showed how to put a ring structure on the set of Witt vectors, in such a way that the ring of Witt vectors over the finite field of order ''p'' is the ring of ''p''-adic integers. ==Motivation== Any -adic integer (an element of ) can be written as a power series , where the 's are usually taken from the set . However, it is hard to figure out an algebraic expression for addition and multiplication, as one faces the problem of carry. Luckily, this set of representatives is not the only possible choice, and Teichmüller suggested an alternative set consisting of 0 together with the st roots of : in other words, the roots of : in . These Teichmüller representatives can be identified with the elements of the finite field of order (by taking residues modulo ), and elements of are taken to their representatives by the Teichmüller character . This identifies the set of -adic integers with infinite sequences of elements of . We now have the following problem: given two infinite sequences of elements of , describe their sum and product as -adic integers explicitly. This problem was solved by Witt using Witt vectors. 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「Witt vector」の詳細全文を読む スポンサード リンク
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